Planes they already have can't really be grounded immediately without replacements. Buying replacements takes time and money. Negotiating contracts also takes time. Pre existing contracts tying a company to boeing probably exist in some places. There's probably some incentive to not drop a somewhat strategic business on a whim. And maybe some people believe that boeing will start pulling their head out of their ass at some point.

And all that would be a hindrance assuming there is a will to stop buying boeing planes, AND move to another, potentially foreign business like Airbus.