I noticed this too with my local Starbucks stores.

It seems boils down to revenue. If too many people sit down and use the area as a third place, then their revenue is capped if people stay too long.

Ideally it's should be a balance between customers and business. Go to the coffee shop, work for an hour then leave, to free up space.

I've also noticed they reduce seating to battle homeless folks from nesting in. It makes sense, I avoid stores if feel threatened from confrontational/aggressive people.