I really don't get why studios do that. They pick some well known franchise to attract the fans of that franchise, but then either figure they can do something better or that fans won't care if they aren't able to stick to the original story?

And so often that "better" they go for is really just different. And there's nothing wrong with telling a different story, just don't try to slap the franchise name on it for the name recognition.

Funny thing is, in some cases they could still do both by just making a new story in the same universe, either one that happens before the video game or after it (and fans would love references to events in the original story in the latter or foreshadowing events to come in the former). Though it's still gotta be a good new story that follows the rules of the universe it's set in.

And to add insult to injury, after seeing the result of this over and over, people walk away thinking movies based on video games can only suck making things harder for those who would do them right.

Exactly, they hated Halo fans and wanted to make something to spite them and it turned out to make no money and they're all out of a job.

Just like Saints Row 4 and Volition...