[MrGreenTea]

Because weaving is simpler and more repetitive than sewing. Sewing is both a pretty precise job and also lots of different movements, angles and very few straight lines. All of these make it less efficient to automate.

If you're interested in the history: it took quite long after during the industrialization to invent a working sewing machine. There are quite a few interesting Youtube videos for example on the history and workings of the sewing machine.