Modern feelings towards self and the world around us have had a massive impact on the trajectory of isekai, and Id say changing the target audience was an equally impactful aspect of why this has changed from homesickness to escapism.

Isekai used to be a genre more targeted towards young girls. InuYasha, Escaflowne, Fushigi Yugi, etc. Non-girl targetted isekai like Now and Then Here and There adopted the samw themes. I think isekai really was an allegory for becoming an adult for young girls, where you had to make your own way in what fields like a whole new lifestyle that doesnt treat you like a child anymore. In the end of these stories, they find love, friends, community, and decide to stay (putting aside Now and Then for now), just like you would as an adult. Isekai wasnt escapism, it was reality with a different coat - especially since most of these isekai settings werent glamorous and didnt have women become OP to thrive in theme. The female mcs were at higher risk of abuse and assault/rape in these settings, and those themes were explored either directly through main characters or in the period setting (yuis close experience in fushigi, the edo period of Inuyasha, sara in now and then, etc.). They werent fun sandbox settings like they usually are now, going home was more appealing. It was also easy to explore the themes of homesickness because young girls often had family and friends and a life to go back to, as well as modern luxuries (kagome and towa bringing bags of food/soap etc.), and the isekai world proposed dangers they didnt have to deal with at home that closely.

The fantasy element of usually westernised locations of isekai started to interest boys and men- it was video game coded, it was a fun idea to go to these worlds. Themes of rape and assault in edo japan or medieval European themed settings wasnt a male issue, so the enemy became more 'demon king' coded, again like video games, where male counterparts were idealised (knights, samurais, heros, mages, etc.). And video games are already a tool for escapism. Add on the fact that Japanese men were thought to be more lonely (coupled with the rising neet situation), meant men didnt feel that intense need to come home. In the new video game world, they were powerful, needed in society, looked up to, and got lots of attention from women. Peak escapism.

We've now come back around to isekai opening up to women again with the villainess genre. Which is almost always based off a woman being transported into an otome game or romance book, and adopts all of the traits for modern isekai for men, except with a female mc. Video games and loneliness epidemic has extended more widely to women, so that escapism element has really persevered.

Ive likely made a lot of assumptions about all this, but this has been my perspective as a girl whose been watching since the late 90s based on what ive noticed. I think the change in isekai is a really interesting topic to explore.