I disagree that track is some weird sidewater - it's been the basis of cycle racing for as long as there have been bikes. It's also much more easily understood and televised. Try explaining the whole load of tactics going on in the road race last week to someone who's never raced, or even never raced at a serious level.
But track cycling has been in decline since the 50 (?), with all the sponsorship money and fan interest on the road. Perhaps except for the winter sixes. Name all the post war cycling heroes, how many of them were track riders?
In the 70s and 80s the track events at a world level were dominated by the state sponsored riders from the Easter Bloc, then after 1989, aspiring riders would choose the road, same as in the West, because there was no money in track cycling.
Then British Cycling spotted a gap in the market, as it were, and now again state sponsored riders are
winning against track riders who have to to get private sponsorship.
Track cycling is easily televised, and some events are easy to understand. But some like the madison is almost impossible to show on TV and that's why it's been dropped. The individual pursuit and kilo wer dropped because I guess a lone rider is seen as boring to the general public, the team pursuit is more of a spectacle.