I don’t think we can see the player numbers, but the number of people following D4 twitch streams has decreased by over 99% since launch. A lot of people played it - but almost everyone who played it has stopped playing it.
Personally I get it. I found D4 to be a fun, but bland and uninspired arpg. It has terrible class balance and skill balance. Despite a lot of promises, there’s almost no endgame to speak of. And there are basically no new ideas in D4 that weren’t already pioneered in D3 or path of exile. The art and music is beautiful, and the first few hours are definitely fun. But it’s not excellent by any means. It’s a bland, uninspired game lacking the depth, creativity and longevity that used to make blizzard games great.