Can't figure this out!

Whenever we walk this way, to the Clock Tower park, there is this 'Kissing Gate' to go through. Jonty religiously enters, goes around the centre gate bit and around the exit. What I can't figure out is why he hasn't realised he can very easily walk underneath the fence as it's more than high enough for him!
He walks and runs across grass so it's not that, maybe it's just because it's the way I walk through it.