Actually the interest in cycling has been on an upward curve since the 80s with the coverage on commercial and satellite channels. The BBC coverage of track cycling is on the back of that and the success of the GB squad starting with Hoy, Wiggins etc.
Golf has always been popular. As a primary school kid I remember the opens won by Miller and Weiskopf, pro Celebrity Gold with Peter Alliss and the A Round with Alliss and I think we can all of a certain age remember Nellie Kim, Olga Corbett, Nadia Commanec (excuse spelling)
Back in the 70s there was only BBC and ITV. Grandstand, Sportsnight, Match of the Day, The Big Match, World of Sport....
They could pick and chose the sports they covered and the "fee" was either nil or negligible.
I even remember the Waterloo Cuo, crown green bowling from Blackpool, with stars like Brian Duncan and Stan Frith.
(I've beaten one of the ex winners)
Let's not forget One Man and his Dog!!!
What we see with the BBC since the satellite channels in particular came along, is that these new broadcasters often build up a sport and then the BBC come along and jump on the bandwagon.
Triathlon is the best example I can give.
The BBC doesn't always win of course because Sky in particular has deep pockets, but that the BBC for years was outbidding the commercial channels for F1 was ridiculous.
Remember as well that there are sporting "crown jewels" that must remain on terrestrial TV skewing the market somewhat.