I think it's because lining of regular mono speedy is glued to canvas like in keepall so it's impossible to sew pocket In dentelle speedy lining is just free layer of fabrick, not glued to canvas, KWIM??? my poor english....
Isn't the mono Speedy just a piece of canvas sewn together with vachetta piping? I mean, like, there's no lining?
If there is a lining, like the Miroir speedy, then it can certainly be sewn on, but if it's just canvas, they'll have to use glue and with wear maybe the glue will start discolouring and I wouldn't want that.
I would prefer that pocket then the little flap pocket we get.