or a system that checks if a player purchased that game
That's what drm is. But yeah, it changed a little when being online became widely spread, so they would verify at every game start, if you bought the game or not, making accessing games even more risky. Some internet outage or the company ceasing to exist will make the game unplayable or even brick it.
If we look at how often Itch was unavailable the last few months, that's just not a user friendly solution. As I said, it is the legitimate users suffering from drm. The non legitimate users do not care, as they are not using the normal game version.
The bestest Denuvo gives a game maybe a window of time of 2 months after release. After that, the game is available on shady sites without all that drm.
I think you might want to ask, if having copy protection will increase sales. I say, it lowers sales, because there are people that do not buy certain games on purpose, because those games have certain drm. Of course I might be wrong here, but sites like GoG seem to be doing fine. And of course, in the sector of Indie games the situation is a bit different. Why even bother with drm. For one that risk of the company disappearing and the drm server with it, is a lot higher. And the target audience is less likely to pirate the game or even give the developer money, after playing a pirated version.
What you might consider is offering added value. That does not even need added drm, but implicitly would only give the added value by having an account with a purchased version. Like cloud saves. Achievements. Online friends and multiplayer matching. It goes without saying that you would need an account and a purchased game to participate.