Why do movies change their ending based on the whims of a handful of clueless viewers (focus group)?

"It's all about the Benjamins, baby," as Puff Daddy explained back in the day.

Usally the focus groups are carefully picked to get the type of audiance members that they are targeting. This has worked great for some movies and killed others. When they did a focus group for the movie "Storm of the Century", the group was almost unanoumous that someone had to survive from the ship. The movie is based on real events and no one survived. The studio almost made them change it before it was revealed to them that it would be very disrepectful to those who lost someone that way not to honor the memory of the crew in telling the true story. So they kept it as was, despite the focus group.

Focus groups can destory certain movies, but I am glad that with DVD/Blu-ray there are alternate endings, deleted scenes and extra features that can open our eyes to some of the damage.

I'd have to say that sometimes the alterations are for the better. They are supposed to be a cross-section of the chosen target group for the movie and viewer opinion does matter.

If it is a movie close to two hours, I will expect something got cut (weird as that sounds) and I wait to watch it at home.

Oh god, I hate it. they ruined pretty in pink! John Huges had to make a whole NEW movie (some kind of wonderful) to make up for his huge mistake. Andie was meant to be with ducky! >.

they don't.

Very few movies are made these days for the sake of making a good movie. They are made for the sake of making money. By changing a film based on the results of focus groups, they hope to appeal to the "masses" and make more money.