Yeah, because the only cost in broadband delivery is the undersea fibre??
How about the core network? High capacity core routers? Firewalls? Datacentres? Power? Optics? Engineering? Ongoing upkeep? Monitoring? Upstream bandwidth? Interconnects? Peering LAN membership? LIR membership?
In many ways their naivety isn't too surprising, we started an ISP last year (https://telcom.io) and the shear scale of the undertaking and costs baffels us everyday!