Could that be because they aren’t as densely populated by users so even if everyone with a phone has no data cap, they won’t overload the network? Which countries were that for example?
But there are other MVNOs out there like tello which also have a 2GB/$6 plan in the US, and other MVNOs which offer unlimited data for like $25-30/mo like visible and US Cellular.
Plenty of cheap MVNOs out there these days.
I'm not a good case study because I rarely use more than 2gb in a month, so Mint would come closer to $10 a gig... :)
There's also 28 GB EU roaming per month included, and 2.23€/GB after that.