I doubt that this will be a compelling reason for you, but the new modems are capable of better speed on 4G LTE than those in last year's iphones. On the 12 Pro, I'm getting 2x to 3x faster download and upload speeds on LTE than I did on my 11 Pro Max (which was no slouch). I do not have a 5G plan, so I'm only accessing LTE.
I love the new form factor: it's been my favorite since the iPhone 4/5. It's much easier for me to grip and manipulate. The 6 through the 11 felt like slick bars of soap (I rarely use a case). I'm on the iUP, so I planned on upgrading regardless. I think that the cameras on the 12 Pro Max will be a very nice upgrade.
Still, I don't imagine that the above reasons will be compelling for you. Sounds like you're pretty happy with the 11 Pro Max.