Spotify is one that comes to mind, originally there was so many triggers on Spotify that were useful, but now there is only like 2 boring triggers. It really killed the IFTTT platform when there was less options from so many of the services.
They went from having less services, but a very deep amount of triggers/hooks to hundreds of services with very little depth. From a deep pond to a wide shallow ocean. And I'm not sure if that's IFTTT to blame, or the services themselves just doing it and IFTTT had no say. Could be a bit of both, who knows. Or maybe services made exclusive partnerships with other services like Zapier, and made their triggers exclusive to Zapier for some deal they put together.
And just to add, at the end of the day, anything automation related that I was doing for professional work was always done on Zapier because they had far better/more options. So IFTTT had always just been a personal playground, noting serious, which is all more reason to not pay for it.