The games they release are complete in them selves, and with 15-20€ dlces every ~6 months they keep the games fresh with new content.
People rarely complain that features are missing from their games until it gets added in a DLC. Then suddenly it’s a mandatory feature.
Question is: Good for who?
IMO compared to what the base game costs, the price of DLC is often inflated. And this is not limited to Paradox.
If you would split up the base game, with all its base content into separate DLCs, the base game would cost a lot more. And this is what DLC is all about. This is a bit a race to the bottom at how much content can we rip out content from the base game and sell it to the customer with inflated prices separately, without incurring too much of a public shit storm.
DLC also plays with peoples completionists desires. Many just want to have the full experience, so they buy stuff, they would like not do, if it was a separate game.
DLC also fragments the community, mods or multiplayer might not work for someone not owning specific DLC. Yet another psychological manipulation into buying them.
So good for company stockholders, but not really good for people that prefer transparent and consistent pricing and quality.