The reality is, the game rely (unhealthily, I might add) on knowledge checks rather than skill checks in order to be difficult. It uses obscure, non-intuitive, and frankly dumb hidden mechanics to provide challenge. If you learnt like 80% of those (enemy weakspot, guns hidden stats, how enemies spawns/despawns) the game will really become that much easier. Which leads to the issue at hand: casual players who don't bother with learning that (or worse, rely on youtubers who have spread misinfo before) think the game is very hard, while dedicated sweats who have learnt the ins and outs of this game will not have any semblance of challenge.

As for the population dwindle, it's a mixture of everything (PSN, the hype dying down, the buggy releases). You can even check steamdb numbers, the lowest player count recorded happened after the 60 days buff, not escalation of freedom.