Why is LAGG not supported on the MB8600 anymore?

The topic says it all. It was supported:

https://forums.xfinity.com/conversations/your-home-network/wan-bonding-to-achieve-speeds-higher-than-940-mbps/6063b16ea12cff7d105aab60

Now support tells me no. 

Xfinity Support has been absolutely zero help in the over 10 phone calls to address this issue. I'm not going to let this issue go until it's resolved. I'm paying for 1200mbit and I'm not going to upgrade my modem and router when this can be resolved by changing a line of text in the MB8600 boot file.

The person who revisited the compatible modems list failed to be aware the MB8600 supported LAGG and therefore a change in the boot file was made.