Because they want their votes. The main objective of every policy the democrats make is to pick up voters. Everything they do is a strategic move to increase their base, doesn”t matter whether it’s good or bad for the country. This is why they are hell bent on granting citizenship to illegals, they want them to be able to vote which would secure another 10 million votes for the dems. They claim to want to give benefits to illegals so they will vote for them if they ever become citizens. They won’t even comsider anything less than citizenship, such as just giving them special status to stay here legally, because that doesn’t give them voting rights and therefore doesn’t benefit dems.

Same concept applies to them wanting to make DC and Puerto Rico states, it would add 4 democrat senators giving them the majority.