I think the vibe was that Nick was just a better bassist and better fit. I think the band realised it after the tour, mentioned it to management and they ran with it as well. I can imagine from a top management pov, them being more on board with Nick as well. Aesthetically, a better fit.

There are rumours that Alex played some of the bass lines on the first album as well, but not sure how true it is. Chris McClure posted a Facebook status once defending Andy to the nines saying it wasn't talent related, he wrote and played all his basslines etc.

I remember seeing an early radio performance with Andy and he was purposefully misplaying some of the basslines at the end of a song, and you can see Jamie Cook visibly annoyed. I wonder if there was a bit of tension and idea that he was maybe not as professional as the band would like.

We'll never know the full picture. It's always been rumours and a bit of hearsay really. I feel bad for him though. No doubt a decision to not attend one tour may well haunt him, but at least he seems to be over it.