Steep Capital cost to be sure. Expensive, overcomplicated and unnecessary to the task
Digital communications can be compromised easily through hardware or software errors, atmospherics and other difficulties
Trunking, encryption, compression and other communications systems have their use and applications. But simple analog methods remain desirable for instant (no delay) dependable and inexpensive universal communications. There is really no need for cloaking such comms as "Approach Medium" or "Highball" or copying Track Warrants, Slow Orders, "Three cars more", "That'll Do!" or "Looking good on that side, AMTRAK".
The VHF channels in use are excellent for the short ranges needed to communicate on stretches of line. This and the number of allotted channels helps to keep someone from talking in Elks Breath, Indiana from interfering with someone talking in Greater Pesthole, NY.
The "alloted Spectrum" is not going away. No one is waving fecesloads of money to take these more or less line of sight frequency bands away, in the manner that Amateur, UHF and microwave bands were stolen. We have seen in the grabs for TV and Cellular channels. And now this mythical ATSC 3 ("Next Gen TV") failure. Jeeze, we just got over converting to Digital and then HD, now we need to scrap everything again and, buy new gear so we can get more targeted advertising? My battery operted TV and Rabbit Ears work when the power has failed and the cable TV is out.
I mean really, folks, no one wanting to profit from targeted advertising and monetization is drooling over 108 - 455 MC. The historic migration of commercial communications from the low band <>20 Mc through 450 Mc is pretty much over. Public service radio has moved into 800MC and above using digital and trunking for dispatch and security reasons.
The use of AM VHF voice comms for air to air and air to ground communications is similar to the VHF FM comms for railroads. There are huge numbers of users, the system works, and changing from one standard to another would be expensive, time consuming, a massive pain to execute changeover, and to what end?
Author's Note:
Please don't give me that Hertz vs Cycles (per second) guff. I've heard it all before. I shall continue to use the descriptive and understandable technological nomenclature that I have for 70 + years. Cycles per Second means something. Hertz was a man's name. Honored, to be sure, but certainly not intuitive or descriptive.
Centigrade means a 100 unit measurement. Who or what was a Celsius? Nevermind, I care not.
Shall we change Lumens to Edisons? What happened to Footcandles?
FM to Armstrong Signal System? Uh nope, bad acronym
Foot Pounds to Ugga Duggas?
Miles per Hour to Furlongs per Fortnight?
Acre Feet to - oh Hades, you get the idea... This has gone far enough.
One Moe Thing - YOU KIDS GET OFFA MY LAWN!