Alan kay was the dreamer, the academic that conceived it. But it took other people to materialize it into something practical.
Those people had different skills than Alan Kay, and they used languages derived by C,like ObjC, java or C++,the C world, which by the way Alan hates with passion.
The C word was much more practical for companies than the Lisp world, you could generate executables that are static(can not modify themselves like Lisp can) and can be sold as a product. They are easier to audit and at the time hundreds of times more efficient(Academics just did not care about efficiency at all like the people who had to actually buy their own machines).
In the end OOP became different to what Alan envisioned, which is a great thing by the way.