Or it selects for easy going people with patience, grit or humility, which seem like positive traits. It is true that companies tend to only hire the suckers that complete their full interview process.
My current company ambushed me with a full interview panel, Gilligan's Island style, when a former coworker invited me to come in for a 3 hour tour. I took it in stride and had fun, and it gave me some additional leverage while negotiating compensation. I remember writing an architecture doc and unit tests when they asked me to code something in an hour and a half. I've been there 6 years and it's been most rewarding for me and my family.
My first job out of school was a solid 8 hours of interviews, and I had a lot of fun during that interview too. I got to work on space ships, and in time made a fortune in equity. I remember preparing a presentation slide deck completely in valid C++ syntax. I also remember taking a red-eye after that interview for another 8 hours of interviews at another company, which I also enjoyed despite having only had 4 hours of sleep.
The 2nd company I worked for decided last minute to interview me for two different roles. That was like 11 hours of interviews. I actually ended up taking the 2nd role because it was a significantly better fit. I brought a large cast iron skillet to that interview, which was a nice ice breaker.
It's true that I put up with a lot of frustrating tasks without complaining, but I personally have zero tolerance for BS. It turns out that the more I push back on BS within an organization, the more I tend to get paid, so in that sense I suppose I am expensive!