Sure, the context of the RLA is intended to protect commerce, but it was also written under the reality that with rail, a competitor can't just slap down some tracks to serve a market where a competitor is on strike. It's the same reason that railroads, although they're partially deregulated, still can't just stop serving a line without going thru the STB for an abandonment proceeding. It's private infrastructure serving the public, but it's not portable. Norfolk Southern can't just start running trains on CSX's rails if CSX is on strike. CSX's tracks are private property, and there are also regulatory and safety issues too numerous to go into. If an airline is on strike, airports are public property. There are no safety or significant regulatory barriers which would prevent Delta from flying a route that United flew before going out on strike. Sure, someone might need an emergency slot exemption at the few remaining slot controlled airports, but that's an artificial barrier to begin with.