Outdoor cafes/restaurant terraces that allow smoking effectively are marketing to smokers. Smokers generally stay longer (therefore may order more), and basically are giving themselves dopamine at this venue, therefore creating associations to possibly draw them back in the future. These places could just not provide ashtrays and could just not allow smoking, but they do allow it, because it's good for business.

If you really don't like it, you could just not visit these establishments. To these businesses, the benefit of allowing smoking doesn't outweigh the negatives (some people not liking it). Obviously you don't not like it enough to just not go there. Not a smoker, but i've never understood this puritanical attitude towards smoking and only smoking. Yeah, it's not great to breathe in an enclosed space, but in an outdoor space, I don't see how much worse it is than car exhaust, air quality, etc.