By that measure, Disc cameras were an amazing success story -- lasting over twenty years.
Nope. That's not what happened nor what anyone is saying.
One might as well say VHS wor the audio cassette were flops because after enjoying 30 years of omnipresence, people eventually found something more convenient.
126 and 110 were massive successes, easily recouping development costs and making large profits for not only Kodak who introduced them but for other manufacturers of cameras and film. 126 did begin to fade in the late 70s but it was still pretty much ubiquitous with the major film manufacturers continuing to support it, all the labs offering 126 processing, cameras still available new. The last 126 camera by Kodak was in the late 80s some 25 years after the launch of the format. While it's heyday may well have been the swinging sixties and by the 21st century it really was on it's last legs with last film produced in 2007....that is hardly a failure considering how many millions of cameras and rolls of film were sold and developed.
110 was, if anything, more popular enjoying immediate success on launch in the early 70s and retaining a decent market share into the 90s. 110 cameras were still available some 25 years after launch of the format and remain available today, though the format is propped up by Lomography. It met with huge popularity especially among children and women who wanted a small camera that could fit in a purse.
126 and 110 film were available in non-specialist shops such as petrol stations, tourist attractions, supermarkets...for twenty years or more. How is that a failure?
Disc was less popular and never really had much of a market share, and the last disc camera rolled off the line in 1989 or 1990, less than 10 years after the format was launched. Most users found the results less than satisfactory and turned to other film formats. Disc didn't even make it into the digital era....which is what finally proved more convenient than 110 and auto loading 35mm cameras.
To argue that 110 and 126 were not successful, or that their level of success could be compared with Disc is just.....ludicrous.