Carnage has a higher budget. It cost more for the sets, costumes, and the acrobats are paid more than the dancers at B&T. The RTU stage was paid for years ago. The Delorean is the same one Doc drives around (or used to) during the day, it's been sitting backstage for years.
If Rocky Horror, which had a shoestring budget, came back we'd see a more extravagant B&T. I haven't verified, but I was told there were about 6 less cast members this year at B&T, but it did feel more empty to me.