PUBG has been getting better and better each year to watch.

Unfortunately, I don't think the improvements have been outpacing the loss of its novelty factor as the game gets older.

Sponsors, player organisations, players, and even I suspect staff like casters are all independently looking at the game right now and deciding that while the game is growing, it still presents a massive opportunity cost relative to other games that might get better even faster (or more stably).

That's all that's needed to steadily disintegrate the scene. If PUBG keeps getting better, but not fast enough, people will still leave in favour of even better investments of their time and money.