Adding a personal experience to @henning's excellent answer.
Many years ago (around 2001) I worked for a company that shall remain nameless, but was responsible for printing the majority of journals worldwide. Although I was only doing reprographics (ie, anything to do with printing / copying that wasn't the journals themselves), just before I left I did some sorting for long term filing (thousands of paper documents being sent off for microfiche scanning).
Being a somewhat boring bit of work, I did end up reading quite a few of them, including a rather interesting email conversation between an editor and the paper's author. Attached were various internal emails where they were trying to find a way around the insistence from the author that they wanted to make a copy available online for free.
End result was basically "the author removed the restriction from the contract before signing, and we can't find any way to force them to change their mind no matter how much we try, so just going to have to left them do it".
While I can't say if there were other similar circumstances with a different outcome, I was going through tens of thousands of pages over the course of several weeks, and visually scanning almost every one, and didn't see any others on that subject. There's obviously also the fact it was around 16 years ago, so things will probably have changed.
While there is a lot of money involved in the journal industry, after basic costs, it's pretty much all profit (that company is sitting on around a third of a billion pounds sterling in the bank, and has well over that in gross profit every year, with well under 50% costs for staff and publishing etc) - but if you want to publish it anywhere else it legally belongs to you, just make sure you only agree and sign to things that you are comfortable doing.