Why does it feel that every boxer nowadays has the same style?

I don't think its just you. Yes, there is some variety with guys like Opetaia etc.

But a lot of top boxers today are Eastern European/ Central Asian and they come from a particular school of boxing - one that emphasizes fundamentals above everything else.

Usyk, Bivol, Beterbiev, Janibek, etc. are products of that system.

The kind of boxers who are highly unorthodox like a Muhammad Ali or a Roy Jones Jr. or someone like Hagler - i am not sure if that type of individuality would be allowed by modern coaches.

There have always been great fundemental boxers and great unorthodox ones.

Its just that today there is extreme emphasis on fundementals which leaves less of a room for individuality and improvisation.

I am a fan of many of these modern boxers but even i will admit that they do follow a similar blueprint.

 

The way You put it - it's a hyperbole, but I do understand where You're coming from.

The world is more interconnected, coaches and fighters can copy one another easier, fighters from all around the world more often train together. It makes sense that instead of having more of independently developing schools of thought, You have more of a one big branch where different ideas are synthesised quicker.
On the other hand, in the past there was a time when professional boxing was very U.S-centered and I think there was no bigger variety at the time (Up to 60s, 70s?). I mean, even something as basic today as southpaw stance was almost non-existent for big portion of boxing history.

It probably all opened up with boxing becoming more global, but perhaps what We've seen after some years of clashes of distinct techniques and boxing schools - is more of a consensus regarding what is the most effective and in result, everyone everywhere is now trying to reach the same end.