I think the cutting off might be the main culprit since as u said multi let's you practice even if you die, and honestly I'm surprised jp fanbase hasn't managed to make the developers introduce a practical feature like deresute's/mirishita's by now.

Disregarding the mess that is below, some new players who come from other rhythm games and don't understand the way scoring works here might see multi as "better to practice in bc u don't die and still get some stuff" initially. I know I was like that a day ago until I learned abt how one's own scoring a affects teammates, and thus started avoiding risks all together, but others might no be as lucky to find said info quickly esp if they don't read guides.