I think that something like this (a flat increase to reload speed) would probably be paired with a reduction in magazine size. I'm guessing that the devs haven't added anything like this because they want to keep a decent amount of downtime in which a player will be unable to shoot stuff - and a faster reload actively reduces this downtime. However, if this faster reload was paired with a reduction in magazine size - sure, there would still be less downtime, but the downtime would (presumably) be more frequent.
However, this would still fly in the face of the (presumed) design intent of the (mostly-)unmitigatable reload times being an active part of the character balancing and such.