That's a good question! Personally, I find the challenge of reducing your ideas to a single submission is part of the fun. But you're right - there's no longer any strict reason for this. I will talk to some other creators and update if people want to make more submissions.
Viewing post in Changes to Tiny Library jams
I think it would be a good idea as well to increase the limit (since looking at the total submission amounts of the past few jams being <20, but the pack total being 36) may be allowing 2 submissions as it would then make it easier to fulfill a theme pack and bring competition to voting /Or/ lower the total amount of winners for each pack to 18 (truly making it tiny expansion & be cheaper for consumers to buy too)? I do love these jams and themes!