These exist in some smart contracts. The problem is that executing a line of code on chain is really expensive. Already quite optimised and stripped back code

These exist in some smart contracts. The problem is that executing a line of code on chain is really expensive. Already quite optimised and stripped back code can cost 50-100 USD equivalent to do something fairly trivial, like swap one token for another. Each of these checks increases the already high barrier to entry, and has little utility for the creators.