I've been hearing about ECS for a decade so it's definitely more then flavor of the month. However the issue is that unfortunately Unreal/Unity are both OO first.
It's definitely been around but I think Unity's (never-finishing) ECS + Rust gamedev community's focus on it has really spiked its popularity/interest lately. Otherwise pretty much every recommendation/engine is OOP-based, with a few straggling extensions/libraries for ECS here and there.
This has been a recognized problem for game devs for a while and recently Unity introduced DOTS to gain performance. From what I understand, doing traditional OOP means going through a lot of pointers to find information. If you put everything into arrays instead, you reduce the time spent looking up things.
