This is in large part due to the EU forcing Valve to allow refunds. I think it was a good change but it is the source of the boring sales.

Before the refunds, Valve used to encourage developers to do flash sales (hour or day long surprise sales) of upwards of 90% off, and similar events. You'd also frequently see that much during the major seasonal sales like the summer sales. There was no risk really for either party because you spent very little on a game and if you didn't like it then oh well, you only spent a few dollars/pounds/euros/chuck-e-cheese tokens on a game so who cares. Conversely, Valve and the game developer had guaranteed income the moment you bought it.

I do miss the pre-refund days as a "patient gamer" because of the insane sales, but refunds have protected us against a lot of things like the cyberpunk 2077 launch, the helldivers controversy, and several other major problems.