Middle managers trading fabrics from major African city (6)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Middle letters of manAGers trADIng fabRics. Why should we take three letters from trADIng and only one from faBRIcs? (Obviously because it’s needed to make the clue work, but it’s a bit unsatisfactory if you ask me)