I'm not sure what's gone on with Matt, but my guess is that he's just missing this last leg.
I've never been super familiar with Bonfiglio, beyond noticing that he has of course worked with Carnie/The Wilsons/Wilson Phillips and that orb (as has Matt Jardine). I wouldn't have assumed he would be a "falsetto guy." I've listened to a few YouTube clips from the beginning of the BW tour and he seems to sound just fine. I mean, I think Matt is by far the best guy they've had in that role so I hope he's coming back. But this seems like a fine fill-in (I would understand if they didn't try to phone up Eichenburger to fill in considering his seemingly abrupt jump to Mike's band a few years ago).
Obviously he's "worked" with Carnie, being her husband and all.
Hence my "of course."
I'm aware he's Carnie's husband. Folks may be aware of only one or the other of the factoids that he's married to Carnie, and also regularly plays with Carnie in many if not most of the touring incarnations she goes out with.
And even being aware of both for decades now, I wasn't specifically aware that he would be a "falsetto" guy. He seems to be doing a solid (if not meeting Matt's admittedly high bar) job.