The freight railroads fought for years to get Amtrak setup so they could ditch their unprofitable passenger rail. Freight trains also don't travel in the same way passenger rail wants to, and rarely stops, and is slow.
The solution is to build parallel lines and more passing sidings and dual track, but that's expensive and nobody involved wants to.
Because freight trains can be really really slow. (I suspect there are a ton of other issues as well--including that you probably wouldn't even cut costs very much.)
The solution is to build parallel lines and more passing sidings and dual track, but that's expensive and nobody involved wants to.
For comparison, the double tracking of Los Angeles to San Diego has been in progress for 20+ years now and is at about 2/3s double track. https://www.sandag.org/index.asp?projectid=260&fuseaction=pr...
And if you really want freight and passenger to coexist you build entirely separate lines (or quad track allowing overtaking).