It's either a paltry amount of money to accept a call, or completely free (unlimited talk). Data is what costs the real money.
If a telemarketeer has to pay for setting up a call, rather than the end-user for accepting it (no matter how small the charge is), then placing millions of automated calls all over a sudden start costing money to the marketeer.
Think of it: the caller has the will to talk to someone - why should (at least in the past) this someone pay for that? The Euro-zone does it the other way round: you want to talk, you call, you pay.
Either way, in both situations with call volumes going down and people switching to data-type connections you see the price of calling/receiving calls drop sharply and as listed above the money telco's make comes from the data plans.
They do have to pay money; initiating a call isn't free.
The receiver has to pay a tiny amount of money if they're not on an unlimited plan, but it's so small that it's not worth considering separately from the annoyance of receiving these calls in the first place.
Back when I didn't have any money my phone budget was $8 a month. Minutes 10 cents a piece, IIRC. People didn't really text very much back then but those were 10 cents a piece as well. Each dime mattered to me very much.
There's also people with plans that only allow X minutes a month.