The purpose of multi bets was either to net in as much profit as the user wants, or simply try to diversify the bet you want, just like how you diversify your portfolios. Though it still depends on the odds ofc, so it still requires a bit of judgment on that point. Honestly researching a team should automatically allow you to identify they're capabilities, letting you bet on multi-bets (or just deciding to go for single ones since you see no possible wins for multis).
But if users don't have a good knowledge base in analyzing, I'm afraid they will just choose the wrong team, which means they can get a loss. It would be fine if they only chose single bets, but what if they were forced to select multi bets where they wouldn't have a big chance of winning.
Researching a team takes time, and without previous experience, it will be difficult to do, and we will have a hard time analyzing it. So we need to know our own ability to analyze so that we don't choose the wrong team.
And that's why it requires proper judgment and not just willy nilly betting. That's no different than gambling after all. Plus, it's as I said, similar to diversifying your portfolios meaning you know what's up with the game, who the parties involved are, and what are the possibilities that would happen. Your sports betting in the first place because you at least know the game, the teams playing, and the chances and possibilities of what could happen, even if your references were past matches only.