I suspect that ARINC429 is the result of a committee which was loaded with rep(s) from a company which was in a position to make loads of money selling the pricey chips that implement the interface.
The first rule for any manufacturer is to load any committee (whose proceeding might affect oneself) with members 
So e.g. the committee which sets specs for domestic appliances will be loaded with Hoover, etc… I was on one of those in the 1980s. I’d say 90% were industry reps.
And in aviation the world is so small; the same dozen characters revolve round and round.
ARINC429 is dead easy and cheap to implement with discrete components but it you have to do say 20 channels it is an awful lot of board space, and the production test (checking the slew rate actually works to spec) is non-trivial.
