Because of the way SSDs work, not only does data not become fragmented, but running a defragmentation utility will actually burn through the program/erase cycles. What warframe does is exactly defragmentation in hopes to clear space between sectors in order to improve loading times (on hdd) here and there. On nand technology the cells can be as far as they can from each other and there wont be any performance difference, it simply wont do anything but waste cycles.
A simple toggle option wont kill anyone but it will make the experience better for many.
I once optimized over 4.5GB while on hdd - no difference at all.