Why do people pre-order in the first place? Stupid.
Convenience, mostly. Sometimes it’s to lock in a sale price that happens between announcement and on-sale date. Scarcity can be a thing, too. Pre-ordering limited editions makes a lot of sense in many cases. Plus in some cases pre-ordering lets you put money down when you have it over time so you’re not shocking your wallet all in one go if it’s an expensive item.
These are some pretty common sense answers in the past 30 or so years that “pre-ordering” (or the 20-30 years before that, “layaway”) has been a popular purchasing option.