No such thing, "learning" in a vacuum describes nothing here. Might as well ask why I am allowed to make noise, e.g. speak, but when I install 5000 watt speakers on every square meter of the planet suddenly it's a problem, and roll my eyes at the inconsistency of not being allowed to "do X more efficiently with a tool".
Did we somehow stealthily develop a neural interface that lets us feed the 'learning' that 'AI' is doing into a human brain? Have we actually figured out how to do that?
No, we haven't. So humans are still learning the same way, but with a new tool to condense and summarize some information. Kinda like a textbook in school. But we don't treat those as human beings with human rights do we?
It's legal in most places in the U.S. to own a semi-automatic weapon that fires x bullets/minute, but not a fully-automatic one that fires 10*x bullets/minute. It's legal for me to send water into my sewer by flushing the toilet, but not for me to pump the larger volume of water in my sump pump into that same sewer.
It's legal for a child to throw a handful of sand from the beach into the ocean. Do you think it should be legal for anyone to build and operate a sand throwing machine that methodically throws all of the sand on the beach into the ocean?
Because it would be absurd for it to be legal to do X, but illegal to do so with an efficient tool. Especially when the activity X in question is "learning".