Actually we did. You could send post cards to enter. No purchase necessary. We received a lot! ;)

fwiw - I follow a number of car YT channels that do giveaways (cleetus mcfarland, etc). They've always mentioned the no purchase required aspect and have a third party company who handle the draw, etc.

Ive found that its always incredibly hidden and requires some kind of paid postage where the non free option is like what OP described