They can build new boosters pretty quickly. New launch/catch towers take a lot longer, and they don't have any redundancy yet. Also they weren't going to reuse their V2 boosters once V3 was ready, so they could learn more by testing things like intentionally disabling an engine during the landing burn or flying at a higher angle of attack.

V3 booster has a lot of changes, including a brand new downcomer, an integrated hot-staging ring, and 3 instead of 4 grid fins. Chances of a RUD are not 0.

If Flight 12 blows up in space, they've already got Flight 13 almost assembled. It might delay them a month, maybe. But if a returning booster destroys the launch pad, it would delay them much longer--maybe a year.

With those stakes, it makes sense to not try a booster catch until they're sure it's going to work.

>Either they can land them or they lose a billion dollars and 9 months when they crash the tower.