That’s a lie.
There are thousands of reasons labels don't want to release some recordings and just because they didn't make the cut doesn't mean they suck at all.
RCA didn't want to put Touch Of My Hand on the record. Was it because the song had a bad production (which is a matter of taste anyway)? No. They were too scared because of its sexual content. And now imagine how many songs like this one weren't included on the final tracklisting of ITZ 'cuz of similar, or even more stupid and less logical causes. Sometimes the sound direction of the album changes drastically, which results in many great tracks being rejected as well. Contracts and complications with the producers is another thing that we should consider. Do you maybe remember why Graffitti My Soul has been rejected? Xenomania wanted it to become a single and Britney's label refused, so they said that Britney unfortunately has to send it back.... and that list goes on and on, most of the times it's not because the songs are bad, I'd say it's really rarely the case.
Also don't forget that most of the leaked tracks are in a demo form, not the final versions so they may be not that good, simply because they're unfinished.