One of the reasons it is so brittle is because it is still very cold even though it is high temp for a superconductor. Many materials will become brittle when cooled down that far. This is one of things people hope for with higher temp superconductors: that they will be less brittle. But less brittle usually also implies that a material changes shape easier and that in turn may affect the superconductivity. For instance when a large current runs through a superconductor that leads to strong magnetic fields and those strong magnetic fields will actively push against each other trying to destroy the conductor. A non-rigid superconductor would behave in ways that are not really helpful. So there is some chance that all materials that exhibit (useful) superconductivity will end up being somewhat brittle, and will need to be mechanically re-inforced.