If an agreement is reached, Oklahoma will be expected to supply water to Texas regardless of how badly it's needed here.
Many cities were on water rationing last summer, due to shortages, and even Tulsa asked residents to voluntarily conserve, as it was approaching maximum pumping capacity. If hot summer weather continues or worsens, there won't be any extra water to spare.
Since Oklahoma can't be assured that it will be able to supply Texas with water in the years to come, I think it makes sense to not make a deal.
I know things are bad in Texas, I spent most of last summer in the DFW area, and it was awful. Not sure what the solution is, but I don't think committing to something that possibly can't be fulfilled even in the short term is the answer. I know a lot of water supplies in parts of the state are dangerously low, and recent rains haven't done enough to raise the levels, which likely means shortages in a few months unless we have a cooler/wetter than normal summer, which isn't in the forecast.