> I don't know what you mean by 'doesn't exist.'
I mean that it's not a separate legal category, it's more of a colloquial thing. Legally, there is property and contract law, and people use that "for investment purposes", but it's largely the same law that applies whether you buy an apple that you want to eat or a share of apple that you want to hold to earn money: You become the (co-)owner.
> A service contract, first and foremost, is a contract between a provider and a purchaser
Yeah, and a bond is first and foremost a contract between a "provider" and a purchaser. And it so happens that bond contracts commonly specify payments in money, but that's legally not all that different from a contract that instead specifies payments in apples or email service or whatever.
> It does have a value, but, much of the time, a B2C service contract isn't a thing that is traded or sold.
Which is relevant to the distinction how? Can you sell a fixed-term deposit to a third party? Sometimes you can, sometimes you can't, but how does that change that it's quite obviously an investment?
> I certainly don't know anyone who is buying email service with the intent of reselling them for a profit, do you?
There is no need to resell for something to be an investment? But even if there were, that doesn't influence the legal status: Even if noone ever resold their bonds and there was no market to do so, that would not excuse the issuing party from paying interest.