They were all sabbotaged and destroyed before completion. In the season 1 episode "Grail", Jinxo (Tomas) gave a bit more description of what happened to at least 2 of them, as well as B4. Now, I seem to recall some interesting elaborations on these events, over at B5 Tech, but I just looked there and I don't see what I recall reading. Also, many in this community dislike B5 Tech for its loose association with canon information. In any case, if it wasn't B5 Tech, then I'm not sure where I read this, but I recall that 3 separate Pro-Earth groups sabbotaged 3 different key components of Babylon 1, without any kind of co-ordination or knowledge between them. When one of the components failed, the remaining undammaged components were reused as part of the next Babylon station, until some of them failed. The final sabbotaged component failed during late construction of B3, when the tech crews powered up the reactor for the first time, and had it blow on them. B4 and subsequently B5, were both constructed under heavy military supervision.