The "dirt" excuse has got to be a bit of a reach. Actually, I think it's simply cost reduction, eliminating the machining step of drilling at an odd angle into a cast assembly, which carries some complexities relative to CNC milling and jig orientation.
I think some bean counter somewhere figured out that each zerk and the associated manufacturing costs a couple of bucks, blah blah blah, and eliminating them wouldn't reduce buyer satisfaction because of the 70K rule. That is, 90% of new car buyers trade up before 70K and never have the opportunity to experience the cost of long-term wear and tear issues. It's a vicious circle sort of thing - people trade before 70K since they "know" there are soon to be problems, which the manufacturers then use as an excuse to engineer subassembly lifetimes at or near 100K.