They changed from the previous version because they figured out how to have ten times as many shards, lower the minimum stake from 1500 ETH to 32 ETH, and remove code duplication that the previous version would have required.

It's incorrect to say they "can't figure out how to make it work." They figured out one way, then a much better way. Right now they have a near-complete spec; the remaining changes are small optimizations. Eight independent teams are working on implementations in various languages.