Because the term was coined by Alan Kay, who apparently later said he probably should have called it message oriented (paraphrasing).

There's also a written conversation you can find online where he disqualifies pretty much all of the mainstream languages of being OO.

A lot of people, like you, say that OO == ADTs. Or rather, what ever Simula, C++ and Java are doing. Some will say that inheritance is an integral part of it, other's say it's all about interfaces.

But then there's people who say that Scheme and JavaScript are more object oriented than Java and C#. Or that when we're using channels or actors we're now _really_ doing OOP.

There's people who talk about patterns, SOLID, clean code and all sorts of things that you should be adhering to when structuring OO code.

Then there's people who say that OO is all about the mental model of the user and their ability to understand your program in terms of operational semantics. They should be able to understand it to a degree that they can manipulate and extend it themselves.

It's all very confusing.

> Most languages choose Simula style OOP

Right, including Smalltalk 76 and 80 onwards themselves. Remember Kay's statement "actually I made up the term object-oriented and I can tell you I did not have C++ in mind, so the important thing here is I have many of the same feelings about Smalltalk" (https://www.youtube.com/watch?v=oKg1hTOQXoY&t=636s); the reason he refers to Smalltalk this way in his 1997 talk was likely the fact that Smalltalk-80 has more in common with Simula 67 than his brain child Smalltalk-72. Ingalls explicitly refers to Simula 67 in his 2020 HOPL paper.

> and reject the things that make Smalltalk different

Which would mostly be its dynamic nature (Smalltalk-76 can be called the first dynamic OO language) and the use of runtime constructs instead dedicated syntax for conditions and loops (as it is e.g. the case in Lisp). There are a lot of dynamic OO languages still in use today, e.g. Python. Also Smalltalk-80 descendants are still in use, e.g. Pharo.

Alan Kay is generally credited with coming up with the term "object-oriented", so for better or for worse, many people defer to his definition and his embodiment of ideas when looking for a strict definition of the term.