I'll answer this as best I can.
The P6050-6077 WUs are all essentially the same WU; 481pts, 2.1 k factor, and all studying influenza (P6020-6025/6040/6041 WUs are similar, though slightly different sized). What you must realised is that this batch is the first one on the a3 core, which is meant to bring in a more efficient way for Folding to be done on multicore WUs. Since they've come out, as much as studying proteins, they've all been helping to develop the core, and the DC project part of Folding@home too.
When the new core (a4) is out, all the lessons they've learnt from a3 should make it a very stable, very flexible core. At that stage, I believe the plan is to put all WUs (unicore and SMP) onto that core, and have a lot more diversity amonst the WUs. Again, the project itself is still growing, and we've come a long way since even last year. This time last year the SMP2 WUs were just coming out.
So it's not as simple as just "Why don't they put other research onto these WUs?" Thinking long term, they need as many results on the a3 core as possible, so they can move towards the next core, which will, we hope, bring all/most WUs onto the same core, and give us some say of which WU we wish to Fold (using small/normal/big options, which don't work at the moment).
Disclaimer: I may have made all of this up.