Multicast on the Internet – How It Works

I don't think you really understand that the Internet is just a collection of many ISPs which connect to other ISPs. Each ISP has its own policies. Also, IP has a single source and a single destination address for each IP packet. Actual broadcasts, from the perspective of IP (broadcast destination address), are restricted to a single broadcast domain, and a broadcast cannot cross a router.

IP does have multicast which is used with a single source, multiple receivers. Like broadcast, multicast is normally restricted to a single broadcast domain. To get around that, multicast routing was developed, but it is different than regular IP routing.

With multicast, each and every router in a path from source to destination must be configured for multicast with the same multicast policies. Also, you would end up forcing ISPs to either always carry multicast traffic for which it may have no users (wastes a lot of precious bandwidth and the ISPs will never agree to this), or the ISPs will need to purchase and maintain special equipment just for the multicast traffic.

Not necessarily. Switches which support IGMP snooping can listen in on IGMP requests from hosts, and send only to those switch ports where hosts have requested to become members of the multicast group. It's a little more complicated if you have multiple switches in the same broadcast domain. How you configure your switch depends on the switch model.

A router will not forward multicasts unless you have configured multicast routing on the router. How you configure that is dependent on the router model.