I checked, and you definitely were eligible for at least the last 2 shuffles. (I didn't check further back.)
I'm pretty sure I was eligible

It is very unlucky: looks like about a 0.4% chance to get skipped 4 months in a row.
That's lower than expected, so I checked: (35/135)*(34/134)*(23/123)*(33/133)=0.3% chance indeed!
By the way, I guess the Timelord hasn't been so close to DT1 for a long time.

He's not the only one: there used to be users with DT1-strength (-14), now (-5) is the lowest.
I haven't seen this before:

That means he's voted into DT1 by only users who aren't on DT1 themselves.