It's a good question and a hard one to answer. Many factors could contribute to needing under 1 year leases. I don't have a good answer, but you can look at your local leases. Near me on apartments.com, the 'short-term' category is ~40% of all the listings. Drilling down a bit into some of those categories, 3 month leases seem to be the lowest, outside of month-to-month leases.

My area may be an outlier, it is covid time afterall. But 40% is not an outlier, especially when it has an option in a drop-down menu.