UFC 170, by contrast, garnered 340,000 PPV buys with a main event pitting Ronda Rousey against Sara McMann, a 135-pound title fight that saw "Rowdy" drop and stop her fellow Olympian inside the first round. The co-main event featured Daniel Cormier's shellacking of Patrick Cummins.
Dave Meltzer provides context:
That's down from Rousey's first main event, one year earlier, with Liz Carmouche. But the drop is hardly unexpected. The promotion of the Carmouche fight, the first women's fight ever in the UFC, was among the best in company history. There was both among the most media coverage leading to a UFC fight in history, combined with a stirring Prime Time shows focusing on the two women leading to the fight.
The McMann fight did have a hook, the first time two Olympic medal winners had ever faced off in a UFC fight. And it took place the week of the Olympics. But that didn't get anywhere near the kind of media attention the fight a year earlier got. A lot had to do with Carmouche, who promoted the fight much harder than McMann. In the arena for both fights, Carmouche was clearly a far bigger "B side" star in the fight, regardless of McMann's wrestling credentials and undefeated status coming in.
UFC 157: "Rousey vs. Carmouche" topped the 400,000 mark.