According to Double-sided M.2 support? (Framework 13), double-sided M.2 drives should work with the Framework 13. Do double-sided drives also fit into the 2280 and 2230 slots of the Framework 16?
For double-sided 2230, no. Not supported.
there is no compatibility for double sided M.2 2230 SSDs in the Secondary Storage slot.
And if you are going to use both slots, Framework recommends a single-sided 2280 to avoid clearance problems.
Otherwise, if you want to use a double-sided 2280, then you need to know the bottom side and topside heights of your SSDs. And compare to the limits listed in Height limitations.
As to why the limitation, they tried to fit more but ran out of space. See Framework Laptop 16 Deep Dive - Memory and Storage
Thanks for the detailed answer and for linking the article of which I was not aware of.