Whatever features browsers have, it does not prevent you from writing native tools.
But browsers don't limit themselves to serving your needs only, and they are not in the business of promoting your approach to computing among their users. Why would they?
Yes, the browsers evolved very much beyond this original purpose.
Again, it did not happen without any reason, it happened for a reason.
The purposes the modern browsers serve apparently are more important to their users than that original purpose!
Indeed, I believe there are obscure browsers that don't support any of this new stuff, and are only good for rendering plain old HTML. They remain obscure for the obvious reason: they cannot be used for what most people use the browsers most of the time.
But browsers don't limit themselves to serving your needs only, and they are not in the business of promoting your approach to computing among their users. Why would they?