That's not how it works. If you're a cell provider, you've bought a lot of gear, permits, licenses, more gear - which cost. If you ever thought spending a couple hundred thousand $ for a big cisco switch was bad, the big mobile switching centers and thousands of cell sites needed are really expensive to commision and operate.
This means you take on huge credit when building the networks, meant to be downpaid over years and decades. If the future revenue stream disappears, you may very well be losing money on your initial investment.
I'm not saying many of the telcos couldn't do with a bit less profit, but don't pretend losing revenue is a non-issue. I'd say its likely a complete restructure of networks and service operators would be needed to really get rid of the roaming charges.
They could also loose revenue from competition because their prices suck. Companies are not entitled to being profitable, they have to compete.
Except in this case there are constraints that prevent full competition. There are only a handful of mobile phone companies that operate their own infrastructure. They constitute a oligopoly and a form of natural monopoly that can more or less dictate prices. The point of regulating utilities is to prevent this.
The classic economic problem with utilities (power, water, phone,gas) is they occupy what is called a natural monopoly[0]. My econ 101 prof explained it thusly: It would be really wasteful if there were 100 different power lines going to your house, yet you'd need at least that many power companies to have something approaching a free market where supply=demand. Not just is the 100 power line outcome wasteful, it won't emerge in a free market.
You can't remove the reasons this happens, you can however regulate it to either somehow cause a competitive market or prevent the monopolist from leveraging their position and price gouging.
Now, obviously cell phone carriers are not a monopoly. They are actually an oligopoly[1], but that doesn't change much and the barriers that lead to it are the same.
One of the big ones is that there is only so much feasible bandwidth to go around. The governments auction it off (in the best case).
In a really free market, anyone could transmit in any frequency, jamming everyone else. Could quickly degenerate into a costest of who jacks up power more.
This means you take on huge credit when building the networks, meant to be downpaid over years and decades. If the future revenue stream disappears, you may very well be losing money on your initial investment.
I'm not saying many of the telcos couldn't do with a bit less profit, but don't pretend losing revenue is a non-issue. I'd say its likely a complete restructure of networks and service operators would be needed to really get rid of the roaming charges.