Just mostly football then! And to be honest. I don't think it's that surprising that horse racing isn't included - just remember who goes horse racing and who makes up the rules (clue: generally speaking, they ain'! usually big fans of football either)!Not just football.
The designation under 2 (1) says all sports grounds over 10,000. If you click on the link, it then goes on to list all rugby, cricket and non-league (including Wembley) grounds where the capacity is over 10,000. So The Oval, for example, is on that first list, but Hove isn't.
Designation 2 (2) lists all PL and FL grounds 'over a capacity of 5,000' - i.e. all of them.
Interestingly, no racecourses are on that list, so it is still a bit arbitrary.