Yeah, but those 0.2M are spread out over almost as large an area as the 1.5; the Greater Helsinki area has a population density of 283 people per square kilometer, vs Uusimaa/Nyland without the Greater Helsinki area at 56. (according to https://sv.wikipedia.org/wiki/Nyland , https://sv.wikipedia.org/wiki/Helsingfors_ekonomiska_region and LibreOffice Calc.)

[EDIT:] So, sure, most of those cars must be owned by inhabitants of the Greater Helsinki area. Heck, I live in Helsinki proper, and I have a car. But... Up until last year, when I still worked at the office in the more central parts of town, my daily commute there was by bus and metro (and will possibly be again sometime soon). And AFAIk I was(/am/will be) far from alone in this combo. [/EDIT]