I haven't seen that as a trend, so I question your sources. (Dribbble isn't really full of people solving UX problems).
In this specific case. The "Play" button overlayed on a video provides near-instant information without reading, about:
- This is an interactive Element
- Its media, not a picture
- I know exactly what will happen when I click it and can prepare (eg turning down my speakers or putting on headphones)
But there's a business problem too. Video has a cost to produce and therefore people need to watch it for the investment to be worth anything. If as the designer you put things in place that look cool but decrease user engagement with an expensive video, your organization quickly stops believing that you have their interests or the user's in mind.
In general, it's worth leaving trends out of UX decision making and instead advocating for the user's needs. Flat design, the hamburger menu, etc are horrible from a usability and accessibility perspective but they've been adopted as "normal" because designers were more worried about getting pats on the back from their peers or likes on Dribbble.