I get the point, but I don't think the analogy holds. Dropbox is a consumer product, so of course convenience counts for a lot. But using Dropbox on your personal computer doesn't expose anyone (except maybe yourself) to being tracked by advertising and social media companies when they don't want to be.
This is maybe just me, but I believe that as engineers, we have a duty to consider ethical ramifactions of the things we are building. Saying "I'm going to do the easy solution, and I don't care about what kind of tracking I'm exposing my users to" shouldn't be acceptible behaviour any more.
We do have a duty to consider the ethical ramifications of what we're building.
But I won't spend hours of engineering time building a share button system because there's other priorities. Say spending that time building a "delete account" button.
There's other more relevant ways to build privacy conscious features than to focus on a share button.
Also, you underestimate share button providers by saying they aren't a consumer product. Your average WordPress user doesn't know (or care) about building share buttons.
This is maybe just me, but I believe that as engineers, we have a duty to consider ethical ramifactions of the things we are building. Saying "I'm going to do the easy solution, and I don't care about what kind of tracking I'm exposing my users to" shouldn't be acceptible behaviour any more.