Presumably, new irregular verbs used to appear, but no longer do. Groups of speakers are less isolated, we have a standardized written language, and demarcations between languages are clearer.
It's been a while since my last linguistics class, but that seems like the natural result of words retaining their pronunciation roughly according to how often they're used. That sounds like a continuous process we should expect to slow as pronunciation change slows (due to recorded media), but not necessarily to stop at some cut-off point.
Why not? Have now we invented all of the words we need, but hadn't yet invented "seen" or "got" in 1200 AD? Then why would it stop now, instead of in 1200 AD?
> we have a standardized written language
But we've had written language for much longer than English has been around
We didn't have standardized spelling, a majority of speakers who could also read and write, or formal grammar education.