Why don't higher end amplifiers come with a separate power chassis?

The two most expensive parts of a solid state power amp?

The chassis, and the power supply.

It’s a cost thing. 
 

Now, as I’m about to build a single ended EL34 power amp, I plan to put the power supply in a separate chassis. Mainly for noise isolation. But, separating the two does come with its own challenges, as had been stated above.

@muvluv What does pro gear have to do with anything as far as this topic goes? You make it seem like studio equipment gave birth to high end audio gear? How about, no…

Yeah.

Car audio is responsible for the ability of speakers to handle highpower.

Right

Small drivers, that can handle higher power came about when higher power solid state amps became a viable option as opposed to the lower powered tube amps that came before that necessitated big, high efficiency drivers in big boxes.

Got nothing to do with car audio…