Had CPR training recently as a high school graduation requirement and the instructor did say that not breaking ribs probably means you're not using enough force to get blood flowing through the body, although this varies from person to person. 2 inches is how far you have to press down (hence why ribs may be broken)

I didn't say you should intend to break ribs, maybe my wording could be better and I'll correct it, but most people are too afraid and don't apply nearly enough force

"about 30% of patients will find themselves with a broken sternum or a fractured rib. In some cases, multiple ribs will be broken but once again this should be considered absolutely normal"

https://www.procpr.org/blog/training/hear-ribs-break-cpr