Why some preamps weigh 50+ lbs?

There's much more to a preamp than a Wiim streamer. 

It’s all about the use of top-shelf premium quality components parts in a premium layout / design, including inter alia, the. use of massive and heavy power supplies required for premium audio performance.

For example ,

- my REGA ISIS VALVE cdp weighs 55  lbs ,,,, not your typical cheap build big box store offerings,

- similarly,  my REGA OSIRIS integrated amp weighs in at 58 lbs,

My BAT phono pre weighs 36 lbs.

Makes me feel better about how much I paid for it!

@mofojo 

Better preamps have the following which adds weight-

Chassis power supply and circuit noise isolation cages or panels.

Perhaps a low noise two chassis design. 

Large, heavier power supply transformers, perhaps two if dual mono. 

Abundant supply of power supply filtering capacitors.

Abundant  supply of signal storage capacitors. 

Heat sinks.

Cabling for multiple switches and connections in and out, balanced and single ended. 

Sheetmetal for a robust sturdy chassis.