It all comes down to economies of scale. Lycoming probably ships a couple of hundred new 0-320's a year. More O-360's, because of Van's, and probably a couple of hundred new 0-540's. In total, maybe 1,000 new engines a year. Even if you go crazy and assume 5x that, the volume is tiny compared to the number of each of its engines Honda builds. That matters. A lot.
Radios, GPS's, etc. Same thing.
We get killed on economies of scale.