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.