Steven, I've had similar issues. What I've done is this:
I created a text file and each time I send a request to be added to the trusted list, I add the date to my file with a note to check it in a month.
When it reaches 1 month and they haven't replied, I send a PM, post to their profile and then update my list: I move the entry back to the top of my list with a note to check it in 10 days.
After 10 days, if they haven't replied, I send an Unresponsive Profile Manager request. And then I make a note to follow up in ten more days.
If no change after 10 days, I send another Unresponsive Profile manager report and annotate "2nd request," then 10 days later, "3rd request." So far, none have made it past 3 requests (leaders at Wikitree are busy part-timers too - but the squeaky wheel gets the oil).
In the end, you get a PM who responds or is replaced.
When they are removed, you usually get an email that the profile has been orphaned. Be sure to log in and adopt the profile and then you're the PM.
The whole game is collaboration. If someone doesn't reply, they aren't collaborating. Time for some new blood.