There are, as it happens, only 13 Democratic senators up for reelection this year. That means that the chances of the first senator being chosen just happening not to be up for reelection is 37 out of 50. After that, the chance of the second senator being chosen just happening not to be up for reelection is 36 out of 49, and so forth. This indicates that the odd against random selection of 6 Democratic senators not being up for reelection this year are 6.8:1. For seven Democratic senators it would by 9.7:1 . . .
I see now that there are ten Democrats on the Senate Judiary committee! That is a horse of a different color; assuming that Dem Judiciary Committee members were chosen without regard to their re-election needs then: No
of Dem odds
senators
1 - 10 in 13
2 - 10 in 18
3 - 10 in 25
4 - 10 in 35
5 - 10 in 49
6 - 10 in 68
7 - 10 in 97
8 - 1 in 13.9
9 - 1 in 20
10 - 1 in 29.49
It's commonplace in statistics to accept a hypothesis if there is a 5% (one in twenty) chance of error due to random chance. One chance in 29.5 may not quite be one in ninety-eight like Cattlegate, but it still is definitely in "Oh, come on now"
territory.
Yes. You are right. It is rather lopsided and unusual.