They're not skimping $2k one time cost on a cubicle. They're skimping on the recurring cost in rent and maintenance on a large facility in which to place that cubicle, plus the cost of that cubicle. My wife was an office manager that worked with a couple startups through expansions, and the costs of office space and office equipment is actually quite a bit higher than you might think.

That said, I still think it's generally a foolish thing to do for many companies and I personally despise open offices. I've recently transitioned to being fully remote, and a hatred of the open office plan was a good part of what pushed me in that direction.