That's a rather weak excuse and not everyone drives to events.
I know I try and take public transit where I can (yes I'm a bit more extreme). If it's not your cup of tea that's ok but the initial question is still valid.
Excel biodegradeable BBs do degrade although slowly, I found it takes over 6 weeks to degrade over the summer (tested a couple of summers ago) at my parents back yard. It was a controlled test, I didn't shoot there.