>there was no regulatory reason to block it
That's a problem, no? If protecting consumers from harm isn't a reason that empowers them to block it, the commission is broken.
"The CPUC serves the public interest by protecting consumers and ensuring the provision of safe, reliable utility service and infrastructure at just and reasonable rates, with a commitment to environmental enhancement and a healthy California economy." http://www.cpuc.ca.gov/
Well they could have (I can't believe I have to say this: monopolies are bad, mmkay?), but they've been captured. https://en.wikipedia.org/wiki/Regulatory_capture
There's that "transition" line again. Still nothing to back up the idea that it's a temporary situation rather than the "new normal." Or more accurately the "new low."
>they can't ban all telecom sales because service might be temporarily disrupted
All? Of course not. But banning ones that create monopolistic / oligopolistic situations in certain markets (the predictable effects of which are higher prices and worse service, including more frequent interruptions of service) is warranted.
In a hypothetical universe where all possible mergers would result in monopolies / oligopolies (and are therefore blocked), that's a feature not a bug.