You're just repeating the same assertion that senior devs are specialists, which is not true.
Not all generalists choose to, or even can specialize. They don't cease to exist once they've accrued enough experience. Nor does having a lot of experience mean you're specialized in any one thing.
You can be senior, have loads of experience, and still be a generalist.
I'm not saying they secretly are working as specialists, I'm saying that knowledge accrual is never perfectly even across skills. Whatever company you work at has their specific set of tools, and the longer you work on them the more you'll know about those tools (i.e. have specialized knowledge), and not the tools in other shops. And even within that list, you'll know more about some of those tools than others.
At a certain point, you would be capable of fulfilling a specialist role in those tools, whether you choose to apply for one or not.
When people say specialists, what they mean is SMEs hired to do one specific, specialized role. You can be an SME in something and be hired into a generalist role, or a generalist hired into a specialist role. Whether you are a specialist or a generalist is down to your job role, not your skills. An SME in e.g. reverse engineering who quit IT and now runs a llama farm/ cafe (the dream) is not an RE specialist, they're a llama farmer.
Not all generalists choose to, or even can specialize. They don't cease to exist once they've accrued enough experience. Nor does having a lot of experience mean you're specialized in any one thing.
You can be senior, have loads of experience, and still be a generalist.