The studio just doesn't have the attention span to do any of the SG range any real justice. I know this is going over old ground, and we're endlessly repeating the same story, but basically if GW spends £100 on one of the SG's, it might make £100 of profit. If it spends that same £100 on WH, it will make maybe £250 of profit, if it spends it on 40K, then it makes £500 of profit, and if they spend it on anything to do with Space Marines, then they make well over £1000 in profit.
So why spend £100 on say Mordheim to only make £100 back, then you can make ten times that ammount by investing on a new range of Space Marines, etc...
We all know that this is the basic business reason why our favourite games are basically left out in the cold. We also all know how GW could get support for these games to actually work properly, but the internal politcs of GW just won't allow that (it's all to do with the regional sales companies refusing to give up control of any sales). So, we are by and large stuck in this limbo until such time as a miracle happens and one of 'our' games gets picked for a revamp.
So if a limited release as with Space Hulk is the only way of GW being able to do something with one of the SG range, then I for one would rather that than nothing at all...