Because that is essentially what has happened now with the SWIFT sanctions.
Cutting off internet from outside world is much more drastic measure, highly unlikely to happen for a prolonged period of time.
Even if it does happen, you can still use telephone lines to connect. [1] [2]
[1] https://www.dw.com/en/european-activists-offer-dial-up-inter...
[2] https://www.france24.com/en/20110201-speak-to-tweet-egypt-tw...
Because that is essentially what has happened now with the SWIFT sanctions.