One thing to consider is that debugInfoEnabled was not introduced until Angular 1.3. Angular 1.3 is also the release that dropped IE8 support. So a lot of public sites stuck with 1.2 or earlier for a long time, which does not have this. So it’s possible that some of those sites were developed under 1.2 and earlier and are either still on 1.2 or recently upgraded to more recent version and no one bothered to add that line.

I will say that I worked on a project that recently upgraded from 1.2 to 1.5 (and we do include debugInfoEnabled(false)) in a large part because of supposed performance improvements, and I noticed none, nor do I notice a difference with debugInfoEnabled(false). Performance improvements resulting from proper coding (minifying, minimizing watches, etc.) do make a difference. I still think anyone running in production should use this line but I am hard pressed to say that it actually matters at all.