I took a look at the backports projects today, and the queues there. The backports queues seem to be pretty siaable, and nobody's really taking the time to take a look at them (73 in Xenial backports, 11 in Bionic, 100+ in Trusty, etc.).
I haven't taken a look in-depth on the backport requests yet, but the key thing I am seeing is that all the backporters are otherwise occupied in working on other tasks.
If the problem is nobody is stepping up to volunteer to take a peek, the question then becomes is it just a lack of volunteers with the proper knowledge, or is it a lack of people wanting to take a look, or is it a lack of volunteers with the proper permissions to do the backports? (I'd be willing to volunteer some of my time out of each week (probably weekends in my case) to poke at the backports queues if I were considered an acceptable member for the team)
It'd also be nice to see what requirements are needed to consider someone to be a backporter, the documentation on this seems nonexistent as does process documentation.