I think the very page you linked explains why they're targeting clothing. Performance clothing is a high margin, high turn around market with low regulation and relatively loose quality standards. Spiber can use this as a test bed for scaling their processes before they can go engage more technically and regulatory challenging fields with confidence.

This is literally one of the few fields where spider silk has a use, but isn't actually super critical. Unlike say on an medical implant. You want to learn about the quirks of QCing spider silk (whoa.. we really do live in the future) on a parka, not in someone's body.