Those 'trendy' villainess and isekai comics are currently extremely popular with the main demographic of Tapas, which is why the front page is so over saturated with them. Tapas is following what currently makes them money. I don't think it's a brilliant long-term strategy - following trends rarely is, you want to have enough diversity to set them - but Tapas is still small, and it's a safe strategy for the time being. So long as they have their finger on the pulse and know when to switch gears, it'll help them grow.
I don't much care for Tapas premuim offerings either - I don't follow any at all - but those artists work at a backbreaking pace to achieve the quality and quantity they have to meet each week. While I'm happy to criticise the lack of variety, and the same-y, shallow quality of many premium stories, I'm less willing to rag on the art.
If you want variety, look to the community comics. There's incredible work being made, some of which is extremely high-quality. Also, look to WEBTOON. Their Originals have more variety than the Premuim comics on Tapas, as they're a larger company with more money to pour into experimenting with what could potentially be trendy in the future, rather than just what's trendy now. And their CANVAS side, similar to the community comics on Tapas, is enormously diverse, with some absolute gold star work.