Despite the fact that it's still not available in the United States
Because the US networks are scared shitless about a service that is free pulling away anyone who would otherwise pay money. But it isn't really free, a TV license is £145.50 per year ($217 approx) but for that you get 11 TV stations, 10 radio stations and iPlayer.
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At £12 / $18 per month it sounds a lot but we get a lot and now we are getting more
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You lucky Americans however can get it a lot cheaper if you use a good proxy software, plenty of free ones out there but it seems all the ones that edit your IP to another country (such as the UK) all seem to cost around $80-ish, so until hell freezes over and Comcast stop lobbying to ban iPlayer this may be your only way. Put it this way, even if all you do is listen to the music it is still cheaper than Spotify Premium.