I think most of them just haven’t noticed when it happened. Same with other products. You need to be a person that has bought the product some times in the past and the type of person to check how much you actually get (the amount of content) to realize something like that when it happens. Even if they realized at some point or got told by another person it probably doesn’t affect a person as much anymore as a person wo saw through that the second it happened since they might think “Well I have been using it the last few weeks/months etc and I was still satisfied”