A combination of things led to the lowest prelims audience in years prior to a UFC pay-per-view show.
Last Saturday's two-hour prelims was split with the first hour on FS 2, unadvertised on the station, and the second hour on FS 1, starting one hour after its scheduled start. The first hour did 153,000 viewers from the more limited FS 2 universe. The second hour, headlined by the Sara McMann vs. Ketlen Vieirra fight, on FS 1, did 418,000 viewers, or less than half of what had been the average for FS 1 prelims in 2017 going into Saturday of 865,000. The previous low mark of the year was 657,000 viewers..
The reasons start with the show not starting on time on FS 1, due to coverage of the Walker Cup golf tournament running long. People who set DVR's to see the match would have missed the first hour of prelim fights.
FS 1 alerted viewers who were tuning in to see the UFC broadcast to go to FS 2. But a large percentage of viewers didn't have access to the station. FS 2 is currently available in about 52,170,000 U.S. homes as compared to 84,421,000 for FS 1.
Before going more heavily into other and valid excuses, another key is that the UFC 215 card may have been the least attractive to the casual fan base. A loss of both the main event, Demetrious Johnson vs. Ray Borg, and a strong heavyweight fight with Francis Ngannou vs. Junior dos Santos, left the main card headlined by Amanda Nunes vs. Valentina Shevchenko. It was expected to be the lowest drawing pay-per-view of the year, meaning fewer fans thinking about the show people to watch the prelims.
There were also four national college football games, including Oklahoma vs. Ohio State that did 8,081,000 viewers, and a NASCAR race going head-to-head. In addition, due to the news regarding Hurricane Irma, The Weather Channel did about four times its usual numbers of viewers and many others were watching the news channels for similar coverage.
Then, due to college football on FS 1 running long, the post-fight show started 30 minutes late on that station, meaning once again it started on the lesser available FS 2 and did only 28,000 viewers in the first half hour before FS 1's coverage of the post-fight show started at 1:30 a.m. and did 172,000 viewers.
The weigh-ins on Friday on FS 1 live did 76,000 viewers, with a 1 a.m. replay doing another 26,000 and an FS 2 replay doing 34,000.