Originally Posted by Big Texas
With the proliferation of online MTM shops (ModernTailor, Cottonwork, MyTailor, et al.), I imagine there must be a place that offers alterations services by mail.
What makes you think so? Firms that offer cheap MTM services are able to do so by outsourcing the labor to very cheap manufacturing facilities. Those facilities are cheap not only because of low labor costs but because of economies of scale - the MTM shirt order comes in, it gets parsed out into specific tasks for the person who cuts fabric, the person who sews sleeves, the person who attaches collars, etc., all of whom are able to work quickly because they do no thinking and do the same thing over and over all day, varying only the specific dimensions of the object they are working on.
Now imagine that you send them the same measurements, but you send them a finished shirt to start with. Now rather than just cutting up a roll of fabric and letting everyone do their jobs, someone has to measure your shirt, then they have to decide what changes need to be made to that shirt to get it to the new dimensions without destroying it. Then the work needs to be done, but the work will be different for every shirt, so the person who would otherwise only attach sleeves over and over again is now having to look at your
sleeves and think about how to go about bringing the sleeve length down by 1/2", and then do it in a way that is a lot slower than just attaching sleeves over and over again. All in, it's a lot harder and more time-intensive to alter your shirt than to just make a brand new one. All you've saved them is the cost of materials, and the raw materials are (relatively) cheap compared to the labor.