Pre-registration is a handy feature on the Play Store that allows you to be notified when an unreleased app is available for download - it actually debuted several years ago. But around a year ago, Google started proactively pushing registration suggestions to some users, meaning you'd be notified if Google thought you'd be interested in a given app or game that had recently entered pre-registration. Engagement with the feature must be low, though, as a number of users have reported in recent weeks that they're receiving more of these pre-registration suggestions (some having never received them at all prior), and it's easy to understand how that could get annoying.
Disabling the suggestions is fairly simple, though, and is resolved with a toggle in the Play Store settings. Simply open the Play Store, pull out the sidebar, hit 'settings,' then 'notifications,' and you'll see the screen below. From there, it's pretty obvious: uncheck the box for pre-registration.
This will not disable notifications for games and apps you actually pre-register for - you'll still get the heads up when those titles launch. You just won't get suggestions for apps and games that you might want to pre-register for, which I think we can all agree is really just glorified advertising. So, if you've been seeing more of these recently, worry not - getting ready of them of is easy, and won't mess with pre-registration notifications at large.