The main reason for the decline of shoujo anime for me really is that girls/women will still consume shounen while boys/men will not consume shoujo as much, so for producers if you have to choose between a shoujo or a shounen you will go for the shounen because you know you will be able to get both audiences while with shoujo the audience will really be majorly female and you will be losing money from half your audience. And that is also why shounen these days incorporate a lot of shoujo tropes into their stories (ikemen, romcoms, etc.) but still do it in a way that is mostly targeted for boys (male protag, big boobs and heavy sexualization of female characters that is not as present in actual shoujo stories), they do it to make sure they will grab both audiences. That is not to say that seinen and shounen can’t do great animes like these (just look at horimiya and skip to loafer), but it also means we get a lot of anime that is trying to do the same but in a very harmful and sexist way (just look at shows like rent-a-girlfriend and the millions of bad isekai that come out every season). So, shounen is stealing shoujo tropes and making them worse (most of the time), and we’re eating that shit up simply because there is no actual shoujo coming out as often as it did before.
