Why would someone sent here by their company for work reasons have both?

They don't have "both", it's literally (usually) issued as single visa sticker whenever you apply for either.

You seem to try to make a bigger distinction between B1 and B2 than the US government does.

Are you saying the form you fill out doesn’t ask you the purpose of your visit?

"Purpose of your visit" in the context of a multi-entry visa with a ten year validity period, is a rather nebulous term.

I don't really remember, it's been 10y since I last had to fill out a DS-160, but I don't think so.

You probably will get asked about the purpose of your _first visit_ in the interview though.

Even setting that all aside, B1/B2 are _obviously_ very often combined together.

"I'm going for a conference, and then I'm going to do some sightseeing on the weekend" is something that, under some very strict and specific reading of the law, would require a B1/B2 visa for example.

If you want to be extremely strict in reading the law, you can't really attend a conference on a B1, and sightseeing would require a B2.