Let’s just say you had a bunch of Audio and video capture card that are pcie. If you wanted to use thunderbolt you’d end up buying multiple pcie to thunderbolt enclosures, have to deal with thunderbolt cables, power cables for the enclosure, and making sure it all is reliable. If you had 3-4 cards that could end up being a mess of wires.

Mac Pro isn’t really targeting normal consumers. It’s a high end product for media professionals. Big companies have budgets for this stuff and professional workstations are expensive regardless of brand.