Shitcoins are such because at least one of:
  1. Premine scam
  2. Poses as decentralized when it's not
  3. Purports to solve problems that it doesn't
  4. Ponzi scheme
  5. Promoted as better than bitcoin
It will be a lot harder to create a shitcoin on top of bitcoin, as the incentives are not there. Bitcoin promotes honest business, a seeming rarity in clown world.