I heard that sites such as Prime Dice makes well over 1,000 BTC (7 million USD) a month. But they struggled a lot during the initial days and spent a fortune on promotional campaigns and bounties before rising to the top.
http://www.starsgroup.com/press-center/the-stars-group-news/the-stars-group-reports-fourth-quarter-and-full-year-2017-results-provides-2018-full-year-guidance
PokerStars did $1.3 Billion revenue in 2017 with $458M Adjusted Net Earnings.
So competitors have to take part of their market share by building something better and investing in the future product offered to players. There are hundreds of casino and sports betting sites that are out there also earning and spending similar amounts of real money.