There's not just a "reason why" that any of us can give you. Each cat's body is different, and while some things are remarkably consistent from cat to cat, other things are different. All you can do is plow ahead.
I will say that some of the biggest zig-zag type spreadsheets I've seen have been in cats that need dentals done - but even that might not explain Shoe's situation. If you have any hint that he needs a dental, if he has bad breath, if you can see any red inflammation at the gumline or any tartar build-up on his teeth, then you might consider getting a dental done. Often is there is anything visible, there is lots that is uncovered once the cat is under anesthesia. Infections can raise blood sugar and getting an infection resolved can often help get blood sugar under much better control.
By the way, it's good to raise these kind of questions in your regular daily thread. Just edit the subject line and put the topic in, then edit it again when you want to return to your regular subject line. The idea is that all the info on your cat remains attached to his daily thread. There's a little more about this in the "
Basics: New to the Group?" yellow sticky. I encourage people to edit their subject line regularly throughout the day - it's your way to communicate with everyone else.
I'd copy the link to this thread and put it in your daily thread for Shoes from today so if you want to go back and find it, you can.