-
Where though? Onto the big old A roads that surround it? Where there's more usable road space because they've been designed to carry high levels of traffic?
That's the problem (and why people use Richmond Park as a through route between Putney/Roehampton/Richmond/Ham/Kingston). The roads that go around it (A305/A307 or A3/A308) are at capacity during peak times, most of them are just single lane roads with narrow sections where there's plenty of conflict already and there's little or no space to widen them to cope with the extra traffic.
Sure, from a purely cyclist centric point of view then making it a no through route would be great, but it's going to cause havoc for everyone else in the area and I'm not anti-driving enough to think "diddums" about that.
Much as I'd love to make Richmond Park (or roads like Priory Lane) a no through route it would just simply push the traffic and conflict elsewhere and not really solve anything.
The time to make Richmond Park a no through route was about 40 years ago.