ISPs routinely sell/share geolocation data for fixed infrastructure; there are many factors that could impact why this is more accurate. In a sparesly populated area, using microwave, point-to-point radios? You very well may be the only subscriber on that first hop from your home network, and that first hop is likely in a geolocation database (this is certainly the case for my cousins farm). In a densely populated ar…
I am not aware of ISPs selling geolocation data in India (will have to look up on that). Yes, my building does have a common on-premise ISP equipment to which all our routers connect.
Note that this may not, and probably does not include customer location data in most jurisdictions. They sell the locations of the equipment they own, which more or less effectively correlate with customer location as I described in my previous comment.