The thing is, XBLA policy means pushing a Title Update costs money (around $40k according to Tim Schafer*), and for an indie company, that means each TU should fix as many bugs as possible, to avoid unnecessary spending. That means testing and testing and reading a bazillion bug reports and try to replicate each one and more testing, and that takes time.
*
http://www.hookshotinc.com/interview-schafers-millions/
BUT, with unofficial patches, there's no money issue, so they can fix things one by one, in order of importance.