Sometimes getting a local SIM as a foreigner is at best a hassle (Ecuador) and at worst basically impossible to do legally (Peru). In other countries, however (such as many EU countries) it can be quite easy.
I have traveled quite extensively in the developing and developed world and in my experience it’s a rare exception not to be able to get a local sim easily. In most cases you can have one before leaving the airport.
Even in the examples I gave (Ecuador and Peru) it is possible to get a SIM at the airport. But you will pay handily for that privilege due to basically skirting government regulations (the most common scenario is that you are given an under the table SIM that is legally registered to some citizen of the country). In a lot of these cases Google Fi or whatever roaming solution you are using is cheaper, and that doesn’t even count the time value of getting the local SIM card and activating it (and I have also travelled extensively and understand that this process can be a non insignificant time sink) vs just turning your phone on and having it work in whichever country you are traveling to.