Commercial aviation works the way it works regardless of whether you think its practical. And you're grossly overstating how many suppliers are on a commercial

Commercial aviation works the way it works regardless of whether you think its practical. And you're grossly overstating how many suppliers are on a commercial aircraft. There are in total an average of 30 tier-1s on a modern airframe, and yes, airlines are expected to work with all of them. Radio Altimeters are typically made by avionics suppliers i.e. Collins, Thales, or Honeywell for Part-25 commercial airliners.