Because it would be totally clear to anyone that reciting the lyrics of a song is not a transformative work, but instead covered by copyright.

The only reason why you can legally do it, is because you are not big enough to be worth suing.

Try singing a copyrighted song in TV.

For example, until it became clear that Warner/Chappell didn't actually own the rights to "Happy Birthday To You", they'd sue anyone who sung that song in any kind of broadcast or other big public thing.

Quote from Wikipedia:

The company continued to insist that one cannot sing the "Happy Birthday to You" lyrics for profit without paying royalties; in 2008, Warner collected about US$5,000 per day (US$2 million per year) in royalties for the song. Warner/Chappell claimed copyright for every use in film, television, radio, and anywhere open to the public, and for any group where a substantial number of those in attendance were not family or friends of the performer.

So if a human isn't allowed to reproduce copyrighted works in a commercial fashion, what would make you think that a computer reproducing copyrighted works would be ok?

And regarding derivative works:

Check out Vanilla Ice vs Queen. Vanilla Ice just used 7 notes from the Queen song "Under Pressure" in his song "Ice Ice Baby".

That was enough that he had to pay royalties for that.

So if a human has to pay for "borrowing" seven notes from a copyrighted work, why would a computer not have to?