European countries used to have fairly high taxes on power and / or displacement, which was why 60s and 70s european cars tended to have such small engines compared to American ones.

It also affected engine designs as e.g. the english RAC horsepower was based on bore, hence the high frequency of undersquare 4s and 6s in english cars even upscale (e.g. Jaguar’s XK I6) as opposed to the oversquare V8s of american cars.