It was 100% illegal. (Well technically schools gave players stipends but that was regulated across the board. But coaches got busted for buying kids dinner or a donor buying a kid a drink etc.)
Its not illegal apart from not collecting taxes or that sort of thing.
It goes WAY beyond buying dinners or sweatshirts. Kids were getting 6 figure signing bonuses on top of like "salaries", parents were given houses nearby so they could see their kids play.