Pure speculation but maybe UA calculated that this guy is more of a liability in terms of benefits, miles, ETCs, upgrades, (maybe getting close to MM), versus future revenue from him so they target him. UA is know for being short sighted so they dont even consider his future revenue. If UA values a GPU at 5K, 25 is 125K. Miles might be 12K. Plus ETCs and whatever the value of the status benefits. Similar to a company trying to push out high paid older employees before they get their pension.
Also, UA banned him from the MP program not their flights. I guess UA may assume he will continue to be loyal to UA and keep flying with them just as much as before without earning miles, status, etc