I think the limit of 3 is because you’re on the free tier. They are trying to transition to a model where they can make money.
I don’t blame them for it, but I did switch to using iCloud Drive instead of Dropbox because I am already paying for iCloud for photos, and the space is so much cheaper for the small amount I need.
Back in the day, I needed less than their minimum tier offered, and sent support an e-mail, because I heard they would give you an exception if you asked.
They were able to give me a cheaper plan with a smaller capacity. A little later, my storage tier was less than the amount they were offering for free, and they stopped billing me.
I don't know if they're still willing to do that, but that gesture earned a lot of goodwill from me.
I don’t blame them for it, but I did switch to using iCloud Drive instead of Dropbox because I am already paying for iCloud for photos, and the space is so much cheaper for the small amount I need.