For all the talk about UFC profits being up, there are a number of reasons for that not related to PPV sales and as well, not likely to be repeated.
They made a ton of money off of MayMac...about as much as they would've made off of a 1 million buy PPV
The made massive cuts of behind the scenes people and even some not so behind the scenes, which saved a lot of money.
They continued to drastically underpay the fighters for the most part.
But, like Frankie said, this is about UFC PPV numbers and the bottom line is that they were tremendously unlucky in 2017 in that their big draws (currently Conor, Ronda, Jones, Brock and GSP if you consider all of them active) had exactly 2 fights between them. If they'd all fought once and maybe some of them twice, we could've been looking at a record year.
As the article shows, more than ever before people are buying the bigger shows in bigger numbers than ever before but are skipping the run of the mill shows more than ever before. I believe this trend will continue to the point where UFC will cut back on the number of PPVs they run because at some point it will make more economic sense to put some of these shows on free TV rather than PPV. And then their PPV average will obviously go up (artificially). But as long as the floor for a PPV is 100,000 buys, this won't happen because UFC is still making money at that number.