That's a good question, but there are 275 characters. That alone should mean 300 mod loadouts, one for each character and a few extra. I have multiple mod loadouts for characters based on what they are doing. They have a "normal" set, a TB set, and a Raid set. Even with the specific characters we use for the Raid, that's 40 mod loadouts right there. Then for TB, there are missions that require you to swap mods and even if it's for 10 characters, that's 20 more mod loadouts.
Those mods aren't coming off just 5 or 6 characters. I have mods coming off 6 different characters for each character I'm using in the TB (That's another 35 loadouts for the Reva mission, and about 15 more for the Zeffo unlock mission.) Then, I have to put all those mods back, plus return the normal set to the character I swapped mods on to. It adds up.
It wasn't a big deal when we were sub 200 characters and we didn't have so many "intracacies" in TB, Raid, even some specific events that require remodding. Upping it to 300 should be a starting point. Especially if they're going to keep releasing 5-10 characters a year, or more. Good question though!