It's a different framing to get rid of figleafs. Everything has to be built so that it actually has a chance of being secure - if your state of mind is "this is exposed to the public internet", BS excuses like "this is only exposed to the TotallySecure intranet" don't work any more, because they don't work in the first place. Perimeter security only works in exceedingly narrow circumstances which don't apply - and haven't applied for a long time[1] - to 99.999 % of corporate networks.
[1] Perimeter-oriented security thinking is probably the #1 enabler for ransomware and lateral movement of attackers in general.