An appointment to the Supreme Court is an appointment for life and it doesn't really require a top notch individual to do the job. Anyone who can serve as a decent federal or state judge can hire five smart clerks and figure out all the Supreme Court cases. There are tens of thousands of qualified and experienced candidates.
The important part is that it's a lifetime appointment. Lots of policies are decided by the court, there's no avenue for appealing its decisions. Republicans are expanding the court's power all the time to get their policies past the elected branches of government. The result is that appointing younger judges eventually stacks the court in your favor and wins political battles for you even as you lose elections.
So the Republicans appoint Roberts (50), Alito (54), and Thomas (42). Democrats appoint Ginsberg (60) and Breyer (56) and Sotomayor (54). And thusly the Republicans maintain power because the Democrats won't accept responsibility for exercising it.
The Democrats' theory is that more senior, proven, qualified people will do a better job for the nation. But it's not a matter of doing a better job anymore. The Republicans have made the Supreme Court a venue for policy by striking down or reinterpreting state and federal laws on development rights, censorship, sentencing, respective state and federal powers, and a million other subjects. They've chosen a president against the will of the people. And they do it all for mostly partisan political reasons.
The essential thing is to appoint a young, healthy loyalist to oppose the Republican abuse of the system.
But Sotomayor is a Type 1 diabetic. I know some diabetics and have seen them age. The life expectancy of a middle aged Type 1 diabetic is 15-20 years shorter than that of an average healthy person the same age.
This is morbid I know, but her qualifications matter little and her health matters a lot. And her health isn't good enough.