it's a popular area for tourists and mountaineers, but also i think it's a lot easier to estimate missing/dead tourists since most of them will be there with tours/companies that have to keep track of exactly where they are.

Syabru Besi is downriver of the border and the starting point for the Langtang valley trek which is probably the third most popular trekking location in Nepal (behind Everest basecamp and Annapurna circuit). I think the tourist data they have is from tourists that are traveling with guides but from my experience many tourists also bypass the official requirements and trek solo so the number could be much higher if the Langtang is affected.

Likely the tourists are better accounted for than the locals. Numbers are likely much higher :(

i understand it as 150 dead, with more people missing, of which 47 are americans.

Nepal is popular for Westerners I think. Maybe for religious reasons?