Its a common answer because its practical. Saying we should work on the 5% sounds good on paper but it does not work in real life. So instead be practical and focus on the main thing (whatever that is) and go from there.
It's easier for a bunch of different teams to individually to tackle 5% problems. Even if some of them fail it's fine. And if you add up all of their improvements it's quite a lot. Whereas if you decide that one thing is the "main issue" and that turns out to be wrong later, you've wasted a lot of time and resources.
"it does not work in real life" What makes you assert so? Our experiences and the acceleration of climate changes shouldn't make us too assertive or negative, but rather humble and devoted to help the environment. It's a huge optimization problem, small gains are big gains. The average person lifestyle is quite a nonsense: an electric toothbrush+razor+vacuum cleaner and many other unnecessary devices, cosmetic products/makeup wrapped in plastics, a car and house with air conditioning, pets(https://en.wikipedia.org/wiki/Pet_food#cite_note-8), plane travels for holidays, 500kg of trash per year. All this should be optimized, from the smallest to the largest sources of pollution. I started with myself: I don't do any of the things listed above, my yearly garbage is 10 empty plastics bags of rice, and a few soap bars, toothpaste, bike tubes wrappings.
