In that case, the gym and trainer were not actually necessary in the first place. Below a specific level of fitness, it doesn't matter what exercise you do. There are safer and more efficient forms, but all that really matters is that you do it and you don't hurt yourself in the process. Those trainers, and gyms, were serving an artificial market that didn't actually need them (like some restaurant waiters, bank tellers, travel agents, etc).

Perhaps a better analysis of the whole situation is a collapse of existing artificial markets that businesses have used to expand beyond their current market.

Exactly

The game is enough for you (and for a lot of people)

And that's in the universe of people that do exercise currently.

But the game doesn't replace weights/equipment (as much as the bodyweight people want to convince it's not needed) or more advanced training techniques (and frankly, several "fitness trainers" are misguided)

But trainers and gyms etc are going to keep existing for people who want to go further, or want to socialize, do something different, have specific training requirements, etc