Who says they are not walking away now? Attendance is down and at least a year or two ago there was a downward trend in viewership. I'm not sure if it has rebounded some or not during the 2018-2019 season.
They aren't walking away when it comes to the tournament. I guess the supposed puritanical outrage only lasts until the first weekend of March?
"As a whole, the tournament is averaging a 6.7 rating/15 share in metered-market households through Sunday, up 8 percent over last year's 6.2/13 and tied for the third-best mark since 1993. Over that 26-year span, only the 2015 and 2011 tournaments delivered bigger ratings through the Elite Eight round (this year is tied with the 2013 and 2005 tourneys)."
https://www.hollywoodreporter.com/live-feed/ncaa-tournament-2019-tv-ratings-rise-elite-eight-1198505