Clowns or cynical manufacturers?

This is the washer from the push button flush valve on our en suite toilet cistern.
The first valve gave up as it scaled up internally and it couldn’t be dismantled.
The replacement valve I fitted about five years ago started leaking into the pan.
Closer inspection showed the rubber was blistering and preventing it sealing. The washer looks as though it is made from a rubber that is not suitable for immersion in water. The replacement was about £4 and postage £3. Sounds like the manufacturer is out to make money selling new valves at £15 each to avoid having to take out the cistern to fit one of a different make.