You're right there - the popularity of most 'mainstream' sports is due to TV coverage, advertising sponsorship
Actually, the two major national survey of sports participation, sponsorship and ratings (ABS and Sweeney)pointed out that there is NOT a correlation between TV ratings and participation.
League is a classic example - lots of TV time, lots of sponsorship, but quite small player numbers.
Netball is another classic example in the other direction - lots of players, very little TV.
Here is the reality of the sports that attract the most live spectators, in rough order. TV results are similar but they are covered in the Sweeney Report and I no longer have access to it;
Australian Rules football
Horse racing
Rugby league
Motor sports
Soccer (outdoor)
Cricket (outdoor)
Rugby union
Harness racing
Tennis (indoor and outdoor)/ Netball (for women only)
Dog racing (for men only)
Here are the most popular adult ACTIVITIES, in order;
Men
Walking for exercise
Aerobics/fitness/gym
Cycling/BMXing
Jogging/running
Golf
Swimming/diving
Tennis
Soccer (outdoor)
Cricket (outdoor)
Basketball
Women
Walking for exercise
Aerobics/fitness/gym
Swimming/diving
Jogging/running
Cycling/BMXing
Netball
Tennis
Yoga
Dancing/ballet
Bush walking
The top 4 most-watched sports are not in the top 10 of sports that people actually do - league and competitive motor sport for example are smaller than sailing IIRC, in terms of actual adult participants in organised events.
This effect is very well known among those who actually formally study these things. It's like the fact that we now watch more sport, but DO less sport. It's like the fact that hosting an Olympics does NOT increase sport participation.
The "if you show it they will come" belief is wrong. Not only that, it may actually harm sports, because they rely on a myth and therefore don't do the things that actually work.