This is a trash can, not an aircraft's engine

It's still on the plane. If nobody tested it at the pressure a plane is at, and it turns out it explodes and injures the crew, that's not great.

It has been tested. It has been sold and used commercially and by the government for $300 before. This is not an example of actual costs being $50k. It is an example of massive incentives on the seller’s side to rip off the one who pays (the US pop), and no incentives on the buyer’s side to care about it.

So borrow a vaccuum chamber, throw it there and certify new company doing trash cans. It won't cost 50k

No, including profit it costs peopably somewhere around 200k for a run of 5 trash cans.

sure buddy, trashcan costing as much as building a custom car

In military aviation, including overhead amd profits? Yes.

Fun fact, if parts are around 30k they can be treated as not worthy of repair. Instead, discard them and nuy a new one.

It's just a piece of metal, how can it explode?

If it is the wrong metal, or wrong enough alloy, merely by touching the things it is in contact with can cause a galvanic reaction. Several airplanes have crashed due to damage caused by galvanic corrosion. The FAA is frequently called a "tombstone agency" because they tend to only take action after a bunch of people die.

https://en.wikipedia.org/wiki/Galvanic_corrosion

Mercury versus aluminum: https://www.youtube.com/watch?v=IrdYueB9pY4

In an earlier life, I shipped items requiring this particular hazmat label on packaging: https://www.safetyemporium.com/12332