How far back are you referring to? I'm definitely not the oldest person around here, but most of my interviews since graduating college were more than casual conversations.
The exceptions were primarily where I was coming in via a referral or they were hiring me for something that was already proven and verifiable, like open source contributions.
There were some companies like Microsoft who were starting to become known for being more intense, but I never came across that.
It wasn't until the mid-aughts that I started to see brain teasers, "real" whiteboarding, and other aspects that started to bleed into standard interviews.
Perhaps the turning point was Jim McCarthy's "beware of a guy in a room", which he meant both figuratively and literally, leading to a transition away from solo or shared offices or even cubicles for software engineers and toward open-plan arrangements. I think that his wisdom led first Microsoft, then the rest of the industry, to treat software engineers not as the darling whiz kids they were in the past, but more a cohort to be closely watched and controlled, as the company is risking a lot on them.
interviews at twitter back in 2010 were 6 hours and that was true even for me when we had an agreement to acquire my company pending the success of those interviews. at the time they had a lot of ex-googlers and they were setup similarly.