satoshi hated BUgcoin
A second version would be a massive development and maintenance hassle for me. It's hard enough maintaining backward compatibility while upgrading the network without a second version locking things in. If the second version screwed up, the user experience would reflect badly on both, although it would at least reinforce to users the importance of staying with the official version.
BU is a BIP, just like SegWit. It is not a "second version".
Bitcoin was designed in a way so that it can be upgraded with hard forks. BU is about removing the block size limit, which was meant to be removed at some point.
Though such bugs shouldn't exist. BU developers are disappointing.