Imo all apps like facebook, twitter, Instagram, reddit, imdb, or anything else that requires network and gives almost no benefits are pointless (and always were).
I see most people are finally getting it and there are less useless rest clients nowadays.
There few use cases for such apps - if you are bad at webdesign and have lots of free time. And second thing - theoretically app requires less bandwidth for requesting only JSON.
Nearly 5 years ago I’ve seen almost hundred tmdb client apps, now - 10-20.
Yeah, that was mostly just a trend thing that died down. In recent years the web experience has developed a lot. Also, I think people just realized having that many clients for a single service is a bit redundant and nonsensical.