Although the short answer is "degeneracy", the longer answer is, I think, much more complex. Tl;dr, English's strongest trait is its ability to use meter and rhythm, which is why these music forms are so culturally dominant, even if some of us might hate them.

Getting into my longer explanation, each language has different strengths and weakness in poetry/song lyrics. As an aspiring music producer who can speak several languages to varying degrees of competency, I think I have a pretty good grasp on the strengths and weaknesses of different languages.

Italian, being one of the "softer" western languages, is good at long vowels and subtle melodic changes. To hear an example of this, listen to any Italian opera song.

Japanese is good at quick consonant/vowel changes, which is similar to Italian in some ways but sounds very different in practice because there is so much of a difference in the rate of change. The language encourages rapidly changing, complex melodies. Just think of J-Pop or literally almost any Japanese-language song you can find.

Chinese is, IMHO, kind of mushy and the tonal qualities of the language make song lyrics a complicated proposition. I believe this is one of the reasons why there is so much symbolism in Chinese poetry. One might be unable to say one thing with pleasant tone combinations but you could say an allegory for that thing with completely different words and tones, vastly increasing the number of options you have. I believe this tells us a lot about both the history of Chinese poetry and also why most of the music coming out of China has such drawn-out vocal melodies, the longer a single word is the easier it becomes to work within a range of tonal limitations.

Korean is somewhere in-between these other languages. It supports quick consonant-vowel changing like Japanese but it's also a much rougher language than Japanese is. This is why so many Korean songs have both fast melodies (like J-pop) but so often feature a "rap part" somewhere in the middle or as a bridge, the language can do both of those things well.

Finally we get to the English language. Not everyone will like hearing this but IMHO, English is particularly bad at song lyrics. There is a reason why most classical western music was written in Italian, it's not because the Italians were more artistic than the English or whatever, it's because Italian was simply a better medium for song lyrics.

What is English good at? It's good at rhythm and meter. This doesn't just include hip-hop and rap lyrics, it also includes things like poetry or the works of Shakespeare (Iambic Pentameter) or even Dr. Seuss (anapestic trimeter).

And this is probably the real reason why hip-hop and rap are so dominant today: it just sounds better as song long lyrics. If you don't believe me, consider what "white" bands and artists currently lean towards, it's either electronic music (which is usually entirely instrumental) or metal music with screamo elements (in which case, the rhythm part comes back into play). Both of these genres are the kinds of exceptions that prove the rule.

As for myself and why I am writing this. I was trying to fit some form of meter into a song I was working on but then I slowly came to realize the above things because I kept running into the same problems. Originally I was just like, "English does meter best, so I'll write lyrics with meter" but it wasn't working very well. Meter establishes rhythm, yet human listening is attracted to the human voice and expects it to play the part of the "lead". Those are two major parts of pretty much all music theories by the way, there's a "lead" part and generally at least one "rhythm" part that supports the lead. In hip-hop, the human voice is establishing rhythm and yet, it's kind of impossible to make the voice not function as a lead too. The second we hear a voice, our attention is drawn to it. This means that the "rhythm" ends up cannibalizing the "lead" even if you don't want it to; and so hip-hop and rap are born when the rhythm and the lead part are nearly the same thing.

Even if we hate hip-hop and rap for its perceived degenerate and perpetually angry qualities (the anger allows for more accent and sharper meter, by the way, although it's not the only way to accomplish that), as an artist I don't see any way around this dilemma. Some languages are just better, artistically, at certain things than other languages are. When poetry was one of the world's dominant art forms, we got the great English poets, the works of Shakespeare etc. But in a time when music has essentially replaced poetry, hip-hop and rap are the closest things that the English language can excel at. And it's inevitable that this music will need sharp patterns to further enhance the meter, which means expressing anger more often than any other emotion.

So there you have my thoughts on the matter. At absolute best, I can't get beyond the "Korean" archetype where meter is used to create a rhythmic bridge in a song, yet at that point it sounds a lot like a Korean song, only worse IMHO because I think their language does that arrangement better than English does. This is because when English does do melody, it's a little more drawn out than Korean is, so the transition from melody to meter is more jarring in English than it is in Korean. Yet I genuinely don't care for hip-hop or rap as music because being rhythm based, I think it usually lacks for any kind of interesting melodic progression. There's often a lot of complex background stuff on loop but this isn't the same as a progression. I also don't like the need to be angry all the time. To me, all of this is really kind of depressing because one thing I wanted to do artistically was try to "kill cringe-hop" because its angry nature can never support a tranquil mind; but at this point I must admit that I don't believe such a thing is even possible for the reasons I've laid out here. It's not as simple as providing alternatives, people naturally want to hear the human voice and our language has certain qualities to it that orient it towards these genres of music.