It was largely the principal of the thing. It's
yet another $x/month, on top of other services being paid for to help service/manage those clients. Example - PM tools. I'm already paying for project management tools - put the files there, damnit. "oh, but I like dragging to my dropbox!". Oh, and someone else uses box.com, and so on.
Again, what gets my goat is partially the payment, but mostly the "it's free for them, but I end up needing to pay to accommodate their use of the service" angle. If they - other parties - were paying for it first, it would bother me less. But raving about how 'free' a tool is which I have to pay for to work with them (and they're using it precisely because it's free) bugs me.
Getting sucked in to a few more $x/month things here and there 1) dilutes where stuff is supposed to live (wrt files) and 2) just becomes a drag on finances. A handful of services can end up going from several hundred dollars in to the thousands if you don't keep tabs on things.
Maybe I'm an HN failure because saving several hundred dollars per year matters to me? I guess my skills must suck - most people can apparently rustle up $300/hr Rust/Go/Elixir project work simply by starting to formulate the idea that they're considering taking project work. I'm not that skilled.