I agree, don't piss with mother bell*...but that is not the same thing as deliberately isolating a massive military asset such that it doesn't get customers for a few hours, or even days. They aren't the local telecom network. That's why its local, and not interstellar.
More than that, prior to Com* showing their hand with the Guards, Com* was no more in a position to idly cut off a house due to their individual assets being momentarily isolated from surrounding populations then they were able to walk up to a house and say "give us this or we will cut your phone lines." Push come to shove the inner sphere coudl and would take Com* out of they proved to be such a threat, ComGuard or no, control of HPGs or no.
Think about it from the view of a major player. You tolerate Com*s weirdness because everyone else does, and because they provide a valuable service so you don't have to. But if they suddenly start trying to dictate how you run your realm, or try to tell you to leave their customers alone to call for help, its not worth the trouble any longer, and ALL the house lords would see that pretty quickly. Suddenly massive numbers of special operatives descend on critical installations across the entire inner sphere, spreading out to handle secondary and tertiary targets over a period of a few months, and Com* is either politely ejected back to Holy Terra, there to be hired for basic repairs, or flat out eliminated as a threat to their realm, and then they spend the time required to overcome the learning curve for running, maintaining, and eventually manufacturing HPGs.
Com* has influence, yes, but if they try to dictate policy to a realm, they lose. Even with the Guard, and cutting links, they still lose. Their outnumbered crap tons to micrograms across the board, and that was before the Clans arrived, and well before they divided their power with the Wobblies. How no one should have let run an ice cream stand, never mind move in and take over contracts for interstellar communications networks. Most especially after Black Box tech, and with pony express set ups in play. Two, three years tops, and the inner sphere has purged Com* and started figuring out HPGs for themselves. And if ROM comes out of the shadows to eliminate the HPGs, then all of those house intel assets (competent of not...) are suddenly focused on them as much as they are each other.
Face it, Com* is a bit of silliness that exists in a very, very narrow field of allowance within Battletech. If they stray too far form that narrow field, they go away. The only thing keeping them in play is deus ex machine allowing them to have far, far superior intel agencies, and the eventual arrival of the Clans distracting everyone from realizing their tech levels were about to make the necessary step to actual create their own HPG network.