Oh my god, people thinking that UFC should go the route of the WWE have no idea what they are talking about. The truth of the matter is that people still very much buy UFC PPV's and if they were to turn Fight Pass into the Network and show PPV's (even if they raised the price to $20), they would lose out on so much money.
Look at the numbers for 2015. The UFC did amazing this year on PPV with 7 out of their 13 PPVs (UFC 182-194) doing over 600,000 buys. Two of those PPV's (193 and 194) pulled in over a million buys EACH. The other 6 PPVs ranged from 115,000 to 375,000 buys.
Now look at the WWE PPV buys. The network was launched in February 2014. I'll start at WrestleMania 30 (April 2014), since that is around the time the Network started gaining steam. WrestleMania 30, the biggest show of the year, did 690,000 buys (plus roughly 600,000 subscribers to the Network).
The prior month PPV (February 14, around the start of the network) had 183,000 buys.
January 14 (the Royal Rumble, one of the biggest shows of the year and this is before the Network came out), pulled in 467,000 buys.
From January 2013 through December 2013, the WWE only had 3 of their 12 PPV events come in over 250,000 buys. Only 2 of those events came in over 498,000 buys (the Royal Rumble 2013 498,000 and WrestleMania 29, 1,104,000 buys).
The WWE PPV model was a sinking ship. Their PPV buy rates plummeted over the years. The year prior to the network, all but 2 of their events drew the worst numbers that the UFC pulled in this year.