They increase the price and I'll cull my Christmas card list and pay my taxes on line, thus reducing my stamp purchases even more.
I mail very little each month and it has been that way for years. Almost all my bill payments are done online. Most of my correspondence is done online.
So the Post Office is not making any money off me personally.
But the Post Office provides me a very valuable service by delivering my mail 6 days per week. I would gladly pay the postage increase for what I get in return from them.