There are prohibitive restrictions on lotteries. This is the same reason when you see "buy now win a chance at _" advertising, there's small print somewhere that explains no purchase is required, and provides a[n inconvenient] alternative to getting chances in the giveaway.

More detail here, a quick scan showed it to be reasonably in line with my outdated knowledge on the topic, at least... https://gleam.io/guides/no-purchase-necessary