Why is Burger King’s marketing gimmick that you’re allowed to modify your orders when that’s a completely normal thing that pretty much all restaurants do?

Being able to get a custom order quickly was not always the case. A commenter says this, but back in the day it was impossible in most fast food restaurants to get a customized order unless you wanted to wait quite a long while. Burgers etc. were under heat lamps and you got what you got, even if it had been sitting there an hour.

If you did want something not available under the lamps it’d often be a 15-30 minute wait.

And that’s how it used to be in the 1980s.