I think the argument is not that people can't imagine paying for multiple services (though I would expect there is a breaking point, since you're already paying

I think the argument is not that people can't imagine paying for multiple services (though I would expect there is a breaking point, since you're already paying your ISP), but that the friction of having multiple bills, multiple accounts, multiple apps on your devices (if they're all supported, etc.) will make the whole arrangement unappealing.