The Baltic station has been in the pipeline for much longer (over 10yrs), with the whole Baltic triangle area further on in its redevelopment phase. It is also about taking some pressure off central station and spreading the density of the city centre along the waterfront. So it wasn't really an either/or issue, this simply had the go ahead much earlier because it had the more favourable CBR, which is what council's need when bidding for new infrastructure funding.
A once a fortnight venue alone rarely commands that, hence the reason why so many clubs have had to part or fully fund infrastructure themselves. Peel have been sitting on much of Central and North Docks for years and have delivered very little in that time.... to create sufficient CBR.
I think BMD was initially heavily reliant on the CWG bid, which would've almost certainly delivered a Vauxhall Stn with approx £800m+ of government funding becoming available. The North end redevelopments have been largely stalled for yrs. It's a bit chicken and egg regards the required infrastructure, but hopefully we'll start to see some movement and the whole waterfront can become better connected into the city centre by metro, and maybe its own dedicated people-mover at some point.