Before you start throwing the toys out the cot and assuming you have understood the issue, it's worth noting the stat about ulez compliance of cars within the zone does not account for many others that drive into the zone from outside. The good news is that may mean the urge for them to drive cleaner vehicles will mean ulez has even greater impact, but the financial impact on these folk is huge and unaccounted for in the stats
If you just bother to read the title of the article I posted (you don't even need to read the whole thing)...
It says "Over 90% of cars driving in outer London".
That includes people driving into London from outside. They are not unaccounted for at all.