I didn’t mean to make the claim that it was an explicit design decision, it seems implied from the design of many relay/standardness rules. “Normal” transactions seem be prioritized so I assumed that was the reason. This always annoyed me as being a bitcoin script enthusiast who liked the idea of hiding puzzles in bitcoin that could be claimed, even if it’s insecure 

 You should read the linked post on why standard transactions exist, it’s not around normal transactions at all, really. Also, any script (in segwit) is standard! You can use any opcode freely.