The short answer is that Paris is and
AFAIK always has been about as "accessible" to GA as London is "accessible" to GA
It's easily 2 hours to the city centre, depending on details.
Very bad planning of the transport infrastructure, really.
The bizjets can get closer, and they can go into Toussus and get Customs (at some price) because I've seen some on the Biggin departures board. But to a jet client a £500-1000 fee is a non-event.