Why do you think that? It clearly doesn't apply to stuff like oil, for instance.
I could give up my phone, but I would be in deep shit if I did it tomorrow. It would take a lot of arrangement to do so and it would piss off my family and lose me work.
People say they're concerned. But the actual number of people attempting to zero the amount of oil they use? Much lower than claimed concern.
Words are easy. Actions have costs that people would prefer not to take on.
How do you know how many there are? Anyone doing that couldn't travel except by foot, buy any commercial products or use any available communication services.
edit - alternatively, there are loads of people attempting to zero the amount of oil they use. They are just using oil to get there.