That's not a good reason because then MIDN shouldn't have to wear the anchors either. I have the same SDBs I wore as a mid and given how little I'll be wearing them, I'm not exactly about to go buy a new set. Also, I'm pretty sure candidates at OCS wear them too.
The chapter says you wear them. The sleeve insignia is what distinguishes you as an officer candidate as opposed to having the class stripes like a mid.
If you still have the generic fit SDBs that were issued to you as a freshman as an Ensign, there is something wrong with that. Note, the OCs at OCS don't have to have that stuff in there for but two months, a big difference from three years.