@LmyBrit so having digested most of what you said, here's a breakdown.
The rights to show content in the UK is fragmented and complicated. Don't shoot the messenger, it's the Premier League who sold the rights as an independent company and nothing to do with the TV companies.
The Premier League has 3 rights holders to live content. Sky, BT and Amazon. These are sold as a contract for X amount of time (the current deal is 2018/19 to 2021/22). They then bid for blocks of matches each season. They are currently on block 1 which takes us up to Christmas so the fixtures are set to the broadcaster and we know who's showing what.
There are 4 rights holders to on demand content (Sky, BT, Amazon and BBC) but each have limitations on the length of on demand content to be shown and for how long. For example the BBC can only make the highlights (Match of the Day) available for 1 week.
All in all, the rights to live content cost Sky and BT £4.5 billion over 3 years with a potential audience of 60 million people.
For comparison NBC in the US paid £640 million for a 6 year deal with a potential audience of 300 million.
That's why it's so cheap everywhere else - they pay a fraction of the cost to show the product.
EFL rights are more complicated. The club's are shareholders in the league so own the rights. They have formed their own system to show live football. Selected matches have been sold to Sky for live broadcast for £525 million. The rest is owned by the clubs and as such is available directly from the club or some have chosen to use a service called iFollow.