Interesting 🤔… I actually have never started a car in neutral, as far as I am aware, but yeah I would had the same issue as I would have expected it to work without the clutch in. (not form the US).
Now not sure if my car would work as in the US or as I expected and just turn on anyway without the clutch in.
I could understand the clutch in requirement. So you don’t leap forward starting it in gear.
Was taught to start a car under minimal load; no A/C, no heat, no lights, no wipers etc. And clutch normally involves hydraulics, so neutral means minimising trans load too.
But also, I’ve been in situations where people drive cars after the clutch has failed. 2nd gear, fire it up, then it’s all about rev matching for changing gears 😆. AFAICT, you couldn’t do it with the US ECU setup…