If they didn't find the XS or XS Max compelling enough to upgrade, the 11 with minor improvements probably won't be compelling enough for them either.
Why wouldn't 6S or 7 users find this a compelling upgrade?
It's the same price as the XS/XS Max, or for the base 11, it's $50 cheaper than the XR.
What do you get for that price?
Well, compared to the XS/XS Max, you get, a far better camera setup, faster charging, faster CPU, better cell signal, WiFi 6, stronger glass, *maybe* more RAM, spatial audio support(I had it on my LG, it's great), faster Face ID that works from more angles, a larger battery(either 3,500mAh or 3,650mAh), a new haptic feedback system, oh and it gets a full 6 years of updates whereas the 6S/7 will stop being supported next year or year after next.
Compared to the 6S, we have:
1.) More RAM(4 or 6GB, iFixit teardown will confirm either way).
2.) More storage(6S tops at 128GB, 11 Pro/Max tops out at 512GB)
3.) Larger, higher res display(6.5")
4.) Far faster CPU(it is literally faster than many entry-level x86 laptops).
5.) Far longer battery life(3,500mAh VS 2,750mAh)
6.) Face ID
7.) WiFi 6
8.) Support for new cellular bands(band 46, band 66, band 71, LTE-LAA)
9.) Triple camera instead of single camera.
Plus, one can trade in the 6S for $120 off of a new iPhone, which reduces the price even more.