Why some preamps weigh 50+ lbs?

My magico q 7 = 740 lbs I have it on wheels and push it around for exercise. I think the krell 700 cx 150 lbs also on harbor freight expensive anti resonance dolly.the soulution preamp > 60 lbs.all used still going strong . My class d flea amps <5 lbs and makes my wounder why I have the other stuff.this is another funny post😁

Marketing.

Why do some preamps weigh as light as a feather? Cost cutting, poor parts/design and build quality results in severely compromised sound quality. 

I guess my Benchmark products don’t qualify as high-end then. Preamp with HPA weighing in at 8 lbs ...

Very humble but BM LA4 / HPA4 has very low microphonics due to the fact that its PCB is physically decoupled from the metal enclosure.  Exactly high-end stuffs.

“Why do some preamps weigh as light as a feather?”

SMPS, chip volume control, light faceplate/chassis are all things that could reduce weight.  The power supply is where most of the weight is - transformers, capacitors, and IEC filters.