In the UK the very first live BTCC race on TV was in 1997, and that was only the 2 races with very little coverage in between for just 1 race weekend!
In 1998 they expanded it a bit with live coverage from 2 weekends, but again was mostly just the racing. I can't remember what coverage was like 1999-2002, but from 2003 the full race day coverage began on MotorsTV.
It's only since ITV4 got the coverage (i think) 6 years ago when we got full race day coverage - that has really helped popularity and more cars/drivers/sponsors come in because of the bigger audience.
I agree worldwide sounds like it needs more coverage, but I don't think it'll get that for as long as the WTCC exists.
I'm not a BTCC anorak, honest...