The new amplifiers is getting warmer and hot

Why the newer amplifiers / AV Processors and receivers is getting more warmer and hotter than the older versions ?
i have 2 1990s amps citation 7.1 and harman Kardon signature 1.5  runs cool compared with my current Parasound A21+
Are you comparing Class D amplifiers with Class A/B ? If so, that's your answer. :)

But doesn't Class D run cooler? More likely that the heavier, more expensive to build heat-sinking capacity is reduced in the newer amps along with more heat tolerant components which allow them to run hotter without damage.
The Parasound A21 is A/B. I had the original, and they ran warm.  I measured the wattage, and as I recall, the idle power was 2x spec.

The other two I believe (but I am not Google) are class D.
@erik_squires  no I’m not comparing class D 
why the newest amplifiers ,AVR , AV processors run warmer than old school ones ?
I know a lot of people is using mini fan on AVR like Marantz Onkyo Denon etc.... I don’t think it was like that in 70s-80s and 90s 
Talk about comparing apples with oranges! What AVR from the 1970's are you thinking of?
Well they did have quadraphonic in the 70's
Have no idea what receiver or preamp was used
All I know is it didn't last long
Because the cpu for the video processor runs 100% unless you have it on economy mode. Most of the excess heat comes from the video processor. There will be a small patch on the top of the chassis that is much warmer, hot even, if you’re watching a long movie. That is precisely where the CPU is. I had this problem with my Denon X3400H a few years ago.

Expect the amp to get very hot by the end of a few hour long movie, and expect critical failure of many of these Denon amps (heavily used ones) from the mid-late 2010s to start failing in a few years.