Similar to the reasons given
here, removing the suppressor adds extra labor time to the item. To give Will as much time as possible to manage the BrickArms business, which includes processing and shipping new orders not to mention designing and prototyping new items, he's chosen to offer the MP7 only with the suppressor still attached.
Really, removing the suppressor is just a few firm presses with an sharp-edged blade away. If you're that desperate for an unsuppressed MP7, hit the drug store and pick up a few razor blades! The MP7 was actually specifically designed to make removing the suppressor an easy Mod for BA patrons to perform should they choose to.
badger
"... and that's when the C.H.U.D.s came at me"
