Sales probably boost people talking about it among their friends/in online communities, and then price-insensitive people that hadn't heard much about it want to get in on it too.
This is a truth. On average - and i will stress
average - an item gets 1.5 weeks of increased sales after a big sale period. The sale gets people talking.
I'm sure many of you have done this one before - you see a new game, and think, 'hey, that looks interesting, maybe I'll get it after I finish my 150 hours in Fallout 4'. But during the 100 or so additional hours you were playing Fallout 4, you happened to forget about the new game, cause 100 hours is, of course, a lot of time to keep something in mind for. But now, come the sale, your friends start talking about that new game, and you're like, 'Oh yeah, I was into that game. Plus, I'm done with Fallout 4 now, and Skyrim II isn't coming out for a couple years yet' And so, now you're thinking about the game again, but with your friends also now offering bias confirmation that you should pull the trigger. With that confirmation bias building into your desire to acquire and possess. So you pull the acquisition trigger, even though the game's not on sale.
As long as what the public are saying is generally positive (or super-negative), significant post-sale purchases is standard behavior.
Even better, though, when you've got a stable of products, and you can do a loss-leader sale. Because, the hardest part is to get people to open their wallets. Once it's open, though, the money just flows out.