My old apartment's intercom system had a bit of advertising material saying it was "computerized, not internet-connected" (or something like that) - it was an electronic system, but all it had was a connection up to the front door entry system, a terminal for the doorman, and the ability to call 911 if you pressed the panic button. No fancy cloud apps to drain your battery and then get hacked.
If an apartment intercom can realize this is important, why can't an oil refinery?
Note that POTS pretty much doesn't exist anymore. Analog phone lines only run up to a point at which they get converted to SIP which then runs over IP (while it's often using "private" networks, it's not air-gapped from the Internet and thus can still be compromised).
If an apartment intercom can realize this is important, why can't an oil refinery?