This is an educated guess. Most amps, at the highest level are monoblocks. Most of the highest level preamps are two box (power supply separated from the amplification). So preamps are amplifying very low level signals and the important part is keeping the high energy power supply away from the low voltage amplification. In amps, the amplification is high power, so keeping the two channels separate is more important. This is so universal… it must be really obvious to designers: monoblocks for amps and power supply separation for preamps.

@emergingsoul Wrote:

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

See below:

Mike

Atma-Sphere MA-3

http://www.atma-sphere.com/en/ma-3.html

There are a few, but amplifiers aren’t usually as sensitive as preamps, so there really isn’t much nee for separate power supplies.

Pass labs does it in their XS series.

It's very expensive and as stated above not as necessary as in a preamp with very low level signals.