VAT is 'Value Added Tax', a form of sales tax.

Taxing sanitary products was portrayed as sexist and also unfair on poor women, who 'needed' those products, even though the taxes raised didn't even come close to the funding received by various 'womens' organisations from Government, and even though re-usable alternatives exist that provide a significantly lower TCO (total cost of ownership).

However, as the UK does have a general approach of not taxing things like food, medication and books it wasn't unreasonable to add sanitary products to that list of exemptions. This was however not permitted under EU rules, which mandated a minimum 5% VAT rate. (Bear in mind that the EU received a cut of VAT revenues).

So the Government were legally unable to remove VAT until the UK left the EU, even though many people wanted it and the rest of us just weren't terribly bothered one way or another.