well I don't really understand the system either, but there were multiple organizations making grants, so if you granted rights to all of them what rights would be left for you - that seems problematic. Also I suppose it was an expensive thing to do so they needed to get grants from multiple places, it seems like any recommendation to change this would be liable to have all sorts of side effects and, in the short term at least (5-10 years) likely to make the system function worse than it is now.
Perhaps there is some negotiation already going on for grant moneys, I would expect so if any grants were sizable, I mean if I am giving you a million dollars to study something I might say before hand these are my requirements and you would probably say yes or no, but maybe some grants were much less in size and involved things like use of facilities. In those cases it would be much more likely to change your value estimation of the grant and maybe refuse because not worth it, but if not worth it less stuff gets made and at some point we are the things working worse than before because some researchers would be like screw this academic career I can just go be a quant somewhere.
I mean as I understand it being a scientist is not exactly really rewarding https://www.zippia.com/scientist-jobs/salary/ so I would probably not want to do anything that made it potentially less (financially) rewarding because while people also do things for the good of humanity and so forth at some point when you're eating your Top Ramen with your disgusting room-mates maybe you might be tempted to change your life course for something with increased comfort.