Not oversubscribing is a cost multiplier at every level. 1 million 1 Gbit customers in a city is going to need 1000 100Gbit connections out of that city and the same for transit, and that will have no impact on pricing? And everything is on average used at 1% of capacity.
And if they choose to gamble, advertising and entering into contracts promising "unlimited data", which they think will be more profitable across their entire customer base? Then they've got to do supply what they promised in the adverts. They chose to gamble that way, and if they lose money gambling that's their business.
I take you are fine with paying 10x or even more for your no oversubscription Internet connection then?
Oversubscription is not gambling. The way it works after your last mile connection is that ISPs look at link usage in their network, city level distribution, city to city, transit, peering, etc, once it reaches 60-80% utilization at peak you start looking at adding more capacity. Bad ISPs (most US ISPs) will let this go too far though.
Sure it is.
If I promise 30 people they can have a burger at my barbecue, but I only buy 20 burgers, I'm gambling that 20 people or fewer will show up.
It might be a reasonable gamble, based on past barbecues - but the guests left hungry will still be hungry, and I'll have broken my promise to them.