People who use GPLv3 want the code to stay open/libre under any circumstances. If this is the goal, why not use the AGPL instead, even for applications which are not served over a network?
This takes away the possibility that people integrate parts of your program into a proprietary network application, even if this seems improbable. There’s nothing to loose with using this license, but potentially some gain.
Only reason I can think of is that AGPL is less known and trusted which may harm adoption.
You can always ask that question. Why not anticipate a potential use on the web and use the AGPL? Why not anticipate people wanting to incorporate parts of your code into their products and use the LGPL? Maybe it could be used within Android or in BSD and you should use Apache/MIT/BSD to avoid license incompatibility? (If your main concern is to give something to the world and not copyleft.) I mean you’re actively prohibiting combining code if you use a strong copyleft license, even if the BSD people have good intentions.
It’s an individual choice on a case by case basis. Obviously people will choose popular licenses more often, despite something being the correct choice. But every license has pros and cons. There is no single answer to licensing.