1KW, 30KRPM Router as a Spindle/Motor?

So, I was in the hardware store today...

And I was looking at lots of pretty nice routers. 8K-30KRPM... Not too
shabby. On most it looks like it'd be pretty easy to remount them...
So.. A 30,000 RPM spindle would be damned nice to have on a mill,
especially if you were running really small bits with high-feed rates,
the motors are powerful - 1KW for many of them, and at router prices,
it's certainly a lot cheaper than the $3000 industrial spindle motors I
drool over in engineering magazines.

That said.. If this is the dream, then where's the heartbreak? What's
the catch?
Why shouldn't I do this? :)