False. If you check Intel ARK, you can see, for example, the i7-2860QM has a max RAM of 32 GB (and this is a processor from 2011). Heck, the i7-8809G supports 64 GB.
We're speaking of mobile CPUs and LPDDR4, here. In other words, viable designs for laptops with good battery life that don't weigh 8 pounds.
my thinkpad is running on 40GB RAM on an i7 just fine
Yep, because it doesn't use a mobile i7. So Lenovo made a different battery/RAM size tradeoff.