It isn't due to a lack of offerings. There are plenty of provides that will happily do so. Anyone who wants to can buy email from Google today! Yet in the face of this the vast majority of users choose not to pay for email.
My current operating hypothesis is that the vast majority of ordinary users value their privacy right up to the point where they have to put a price on it. At which point a handful of nerds (like us!) are willing to pay, but most people happily trade their privacy for services instead of involving money.
With that said, might this be viewed as a distinction without a difference? If the provider puts a price on their service, the consumer evaluating this price must decide if they find it acceptable. This is necessarily going to involve some amount of implicitly calculating their price for the service, isn't it?
I'm not sure what you mean by "buy email from google today." I don't want to "buy email," I want to pay them to not serve ads or track me when I use their services. That includes far more than email, I'm talking about the whole ecosystem like Android, Maps, Search and so on. Surely $120/year from me is worth far more than they're getting in ads, right? I dunno.
I can also see the criticisms now: "privacy isn't a luxury only for rich people!".
But if you do so, does that mean that Google won't track you? Even if Google claims they won't, can you trust them?