The lead-up to UFC 177 was a trainwreck in almost every way imaginable. The card went from the spot for a planned rematch between Jon Jones and Alexander Gustafsson to a pair of title fights anchoring the card with Demetrious Johnson facing Chris Cariaso and the rematch between Renan Barao and TJ Dillashaw to TJ Dillashaw taking on Joe Soto.
So, to expect the card to have done well on pay-per-view was unrealistic. It looks like the card will come in on the very low end of UFC pay-per-view numbers..
Over at MMA Fighting, Dave Meltzer says that the estimate for the card is 125,000 buys and gave somfe insight into what that number ultimately means:
The first conclusion one would come to is that as long as UFC has a show about once a month, there are 125,000 homes, or at least groups of people, who are big enough fans that they are not going to miss a pay-per-view. And perhaps the cancellation of UFC 176, meaning it was eight weeks between shows, may have had some people ready to get together for a big show, even if the show, from a star power, wasn’t up to the usual standard.
Another thing to look at is the communal aspect of pay-per-view and people making plans. Pay-per-view is generally not something people watch individually, and thus, there are plans involved. While Dillashaw vs. Soto was hardly a fight one would have expected to do even 125,000 buys, Dillashaw vs. Barao was advertised for weeks, and would have been expected to do a larger number than that.