Which is not so good cause in reality those are really shytty numbers for network TV. UFC on Fox pulls those numbers with nowhere near their top stars as headliners
UFC on Fox 19 did 2.5 million views with Glover Teixera vs Rashad Evans as the headliners
UFC on Fox 18 did 2.68 million views with Rumble Johnson vs Ryan Bader as the headliners
UFC on Fox 17 did 2.78 million views with Rafael Dos Anjos vs Donald Cerrone pt 2 as the headliners
^^^ All of them are known fighters within the UFC world just like Thurman/Porter are within the Boxing community. They are on similar levels in their sports except Teixera, Evans, Johnson have all headlined a PPV while Thurman/Porter have yet to.
Boxing pulling 2.5-3 million views with Thurman/Porter (who aren't nowhere near the top stars in Boxing either) is impressive as well. I could see if it was Manny Pacquiao, Floyd Mayweather, Miguel Cotto, Canelo Alvarez, GGG fighting in a good matchup on free tv....but it's not. It's Thurman and Porter. They aren't top draws in the sport so them doing 2.5-3 million IS impressive.