The amount the payphone owner charges the calling card company is regulated, but you are correct that they can mark it up as much as they want. I would think that the obvious solution would be to find a calling card that doesn't. It's not like there is a shortage of options.
I get the impression you haven't used a calling card in a while. The ones I use have a flat per minute charge from normal phones, and about a 55 cent per call surcharge from payphones.
You're utterly confusing causes and effects. Three things happened at about the same time that were bad news for traditional pay phone service. The first was the plummeting long distance rates due to IXC competition. When long distance cost 30 cents/minute and local payphone calls were a dime, there was plenty to share with the telco to compensate the payphone owner. The second was cell phones, which now carry a whole lot of calls that used to be made on pay phones. And the third, which I presume you are referring to, is COCOTs.
It's true, COCOT providers have sometimes competed on the basis of how much customer revenue they can kick back to the owner of the location where the COCOT is located. But I don't see that any more -- now I typically see COCOTs that charge about the same or maybe even less than telco payphones. I see plenty of COCOTs that offer flat rates as low as 10 cpm for some international calls, something that Ma never gave us.
R's,
John