The VSFS ratings dropped much more than normal for a lot of reasons, not just people's lack of interest.(mostly from it, but still)
RATINGS 18-49(The most important one for publicity)
2009: 2.9 8.3million viewers
2010:9million viewers
2011:4.6 10.3million viewers
2012: 3.6 9.48million viewers
2013: 3.4 9.72million viewers
2014: 3.4 9.29million viwers
2015: 2.3 6.60million viewers
The 2014 show registered 3.2 rating 18-49 and it was followed by Christmas specials and those registered similar ratings.
The 2015 show followed two repetitions that rated lower than the fashion show itself, (1.4,1.3).
There is also decline of VS's popularity, and people running away for the Kardashian name and perhaps the most important of all: TV's viewing own decline.
The numbers of TV Audience are at its low with Network's shows media average rating being 1.5 or 1.6 (minus CW) WHILE 2 or 3 years ago it was 2.4 or 2.5. These 2.3 ratings and 6.60 million viewers don't count the ones that watched it on CBS All Acess and online. In a time where online viewing is getting popular by the day. Every year shows are hitting their all-time lows(even The Big Bang Theory and Empire now).
I am not excusing the show tho, they deserved they low poor ratings for an awful show and I hope they do get their shit together, I am just saying that the decline probably wasn't as hard as everyone thought.