Why does nearly every category have sellers restrictions?

I am a VERY new seller. New as in I saw a TikTok less than a week ago showing someone buying a product on clearance from Walmart in bulk and flipping it on Amazon and then decided “Gee, that doesn’t seem hard. It actually seems fun!” so I paid the money for an Amazon sellers account hoping to flip deals that I found as a fun side gig.

I then went to Target today, hoping to find some items that were flipable.

Found one in the baby section. Scanned it in the app. Can’t sell it because there’s a sellers restriction.

Went to Toys next, found a few nice flip candidates. No dice there either. All locked out because of sellers restrictions.

Candy, music, same story. I then gave up. I can understand why Amazon has some sellers restrictions. As someone with no official affiliation to any distributors and no documentation other than a Target/Walmart/random store receipt, how do I get around them?

Much appreciate any help!