What failure exactly?
OOP has flaws but it has certainly proven to be extremely versatile and adaptable over these past decades since even today, it's still the dominant paradigm to solve modern problems in computing.
I have to admit I never really got further than the first 5-10 minutes or so. My first computer experiences are from the late 80s (and indeed didn't have a mouse) but this demo is so old, I kept having to mentally translate for myself which bits might have been new or ground breaking, and which just plain archaic. I keep meaning to watch it in full some day, but the first bit that I saw, I keep feeling I'm missing something important. People are lyrical about this demo (hence the name!), but I don't quite feel it or something. Then again, while I appreciate the great work of engineering that went into it, I'm not really one to sit down and watch a documentary about the moon landing program either.
Maybe somebody here knows a good link or article about The Mother of All Demos that explains which things I should be in awe about and why they were so novel then?
Part of it kind of looks like a simple database table system, which reminds me of a stupid story from my childhood. When I was young (~1990 I guess), I was playing with the MSX BASIC on a friend's computer whose family had a farm. They wondered if I could write anything to keep track of their cows or something--sure thing! (though I really preferred to write graphics code, later joined the demoscene, way more fun). Now I had no idea about business or their requirements (let alone requirements engineering), so I just wrote some whatever that let them enter data, but in the back of my mind I wondered how this was going to be useful for anything. Neither did I know (yet) how to actually save the data so it'd be available after reboot, which was probably a big reason for my doubts. And they were still impressed (that it could repeat names of many cows, I guess). I never finished it (nor any idea of what "finished" would mean).
Ivan Sutherland's Sketchpad demo - Object oriented graphics using a constraint based system (https://www.youtube.com/watch?v=6orsmFndx_o)
Douglas Englebart's demo - too many innovations to list, but includes real time collaboration (he demoed in a convention center while the system ran 30 miles away in his lab, connected by a leased line operating at 1200 baud!). People think he just invented the mouse, but the overarching theme in his work was augmenting human capabilities... http://dougengelbart.org/firsts/dougs-1968-demo.html
One of the things that consistently impresses me about 1960s computing demos is the clarity of meaning and lack of jargon.
I'd argue that neither of these are really a good measure, I'm more interested in the concepts that a source file captures than its size in kb, because these concepts correlate directly to how easy it will be to evolve that code base in the future. There is a point of diminishing return in trying to make the code too compact, which basically means you're optimizing in one dimension at the detriments of all the others.