Without trying to sound like a complete wet blanket, here's a few reasons why I think track has issues:
There are not a lot velodromes left in the world, and more than a few of the ones that are left are in need of help.
People can't just go off the street and pedal in. You need a track bike, and in some cases for steeper velodromes, training, which puts a lot of people off immediately (You can go ride your typical office park crit with most any road bike, but honestly even those have low turnout numbers compared to something like a "Gran Fondo"). Yes, there are rentals and classes, but compare that to say Tennis, BJJ, or other less competitive sports, it's a lot. Before the fixie boom hit around 2006-2007, getting a fixed gear bike in of itself was difficult.
Most people are very intimidated by the concept of racing in general (like actual racing, not just "I'm going to try and do a 5k" kind of thing), and can't handle the competition. I saw this all the time when I used to work on and race cars. "Hey why don't you go bring the car up to the track and see how it really goes?" and they would stammer around and make excuses about "Getting ready" or some other stream of excuses "It's too expensive!". It's way easier on the ego to buy the gear, rather than actually be humbled by someone on a cheap bike with box sections.
It's visually not as stimulating compared to something like road cycling, mountain biking, or cyclocross. There's not a lot of "cool" appeal to most people versus like doing some downhill mountain bike ride with huge jumps, or whatever is on a Mountain Dew ad.
There is very, very little promotion for it (at least stateside) versus the aforementioned other than the requisite Olympic footage you might see on some highlight reels. Almost everyone I've ever talked to about what I do on Wednesday nights looks at me blankly and I have to go "Oh you ever seen the Olympic thing with the big oval and you pedal a lot."
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So what can we do to make it grow?
IMO Any area with an indoor velodrome should really hammer hard on the spinning crowd. I think the Detroit 'drome is a good step forward and trying to keep things fresh in people's minds. Some televised/streamed events wouldn't be so hard to do, but there's so much media out there that it's hard to keep track.
Be positive and try to bring more people in. Every one on the track should be kind of a mini ambassador.
Leave the BS at the door. Thankfully most track racing people are really nice and encouraging.
It's hard challenge with zero budget, and a lot of other activity competition.