There are probably a few reasons. The hot climate of the middle east would probably be part of it. I would think another issue would be that cloth was expensive! Robes and Tunics if done right waste very little cloth. It does take more sewing, but while hand sewing is time consuming it is nothing compared to spinning and weaving by hand.
Remember today cloth comes from huge factories using state of the art equipment, in the time of the Gemara state of the art was a drop spindle and a warp weighted loom, bot of which are very labor intensive to use.
Of course there could be a lot of other factors too.