I recently run several thousands Maps requests and can say this is pretty common, and this is actually usual behaviour of Google Maps UI, if one goes and checks by hands. Serpapi just returns what Maps give it. And if we go to almost any search result of Maps in native UI, and run through all the pages by hands, we'll eventually have wider and wider query coverage, that is map will be zooming out by itself.

My script had to check coordinates of every subsequent page results, and if they were too off, stopped pulling next pages.

Can't say if this is really good or bad, but it just replicates Google Maps behaviour for sure and probably should be left as is.