How far can they go reducing the emissions before they are left with nothing to vote for.
This is definitely the case with automotive tailpipe emissions. Electronic engine controls have reached the point where engines can now meet the tailpipe emissions standards (apart from CO2) from 20 years ago with no post exhaust treatment (read: expensive catalytic converters and their network of O2 sensors). In many areas new cars actually clean the air; the exhaust fumes are cleaner than the ambient air.
It’s gotten a bit ridiculous, some of these engines are literally designed around the catalytic and their warming cycle, at great expense. There needs to be some perspective on the cost/benefit of eliminating that last 1% (but good luck having that discussion, because the Green Lobby treats the introduction of any perspective as if it would involve going back to 70s era Los Angeles).