What you said is not exactly true.
What you said does happen but not because of or due to DPI on encrypted VPN traffic. There are many other ways nation states can simply track people including physically and through meta data from apps and services they may be using. Not to mention sophisticated zero day malware like Pegasus.
Also, they heavily block VPNs (and/or Tor) altogether because they can’t get inside the encrypted traffic (to perform DPI) so many are forced to not use one in some extreme cases. Ergo, the tracking.