The democrats essentially apply a litmus test to judicial appointments and make sure all of their appointments are liberal.
The GOP fails to realize they can do the same, and as a result, sometimes nominate judges that do not reflect their judicial philosophies. Moreover, many Republicans are far more liberal, like Bush, than the democrats portray them. So it is not that surprising, for example, that the elder Bush nominated a liberal in Souter and also a conservative in Thomas.
Dems don't tend to nominate 2 individuals of such disparate judicial philosophies.