>>76713723 (OP)
It's basic common sense. If you can even do lots of sets of reps, you didn't actually push yourself to the limit.
If you truly pushed yourself, you could only do very few sets at that intensity.
Just because you spent 3x more time at the gym, it doesn't mean you're going to get more results. I learned this when I was doing Stronglifts 5x5 years ago.
I got more progress in like 3 months just by focusing on my strength and compound lifts than most do with all these stupid and useless machines.
My workouts would take like 30-45 minutes and were super simple, no need for overcomplicated programs with like a dozen different exercises.
And SL5x5 isn't even considered a pure strength training program. There are many with even less volume.