It's almost certainly because it looks nice to the AAA investors when you say you've secured your product so people will have to buy it. It doesn't matter how effective it actually is, it's all about appearance. In terms of long term strategy, these companies don't want you to have ownership of their games, and DRM is one method on the step of doing so. Tying their games to always online when completely unnecessary? There's another. I'm sure they know that if they didn't have it, it might sell fractionally better, but the long term goals that they are playing towards is games as a service and every roadblock they can throw in the way to make that seem normal is going to happen.
In Monster Hunter's case, they were retarded and constructed the DLC such that everyone needs to have the expansion installed in order to play together, so even if you haven't bought the expansion, the data is literally sitting on your disk. The only thing you need to access it is a fake license or a bypass. Both which came out the same day. Capcom isn't even running account verification on their servers because their servers are literally a middleman to connect p2p communication for multiplayer. You can run a cheat to unlock the content, access it online, and Capcom would never fucking know. It's no wonder they are ramping up their anti-tamper: they're idiots who gave out the expac for free without any way to make sure you weren't supposed to have it.