Those governments can only block so many IP addresses and they have the big VPN providers in their crosshairs.
You obviously haven't considered DPI. I have been to Iran in the past and OpenVPN to my own server in Europe was entirely blocked, no matter what protocol/port combination I used. I could see the initial packet exchange (tcpdump), and after a short while the connection was identified as illegal and dropped, and the protocol/port combination entirely blocked from there on.
However, they did allow PPTP (possibly because it's so insecure), and SSH. As a side note, I haven't seen any try to do MITM on SSH.