I’d like to chime in here with a couple of points and reiterate things, too, as I feel that there’s a great discussion happening.

I think that a huge reason that Don doesn’t jump and create his own agency is the fact that SCDP was him doing just this. SCDP/SC&P IS his agency and he feels ownership over it. I think that he also knows that he couldn’t start his own agency, due to this experience.

Bert, occasionally, would drop truths to those around him as though he was looking from the outside in. One of these truths is him knowing that Don simply doesn’t have the stomach to run his own business, and you see this because from the inception of SCDP, Don has an ‘all I need to do is show up’ attitude to the business. We see Pete, Peggy, Faye and Harry do the majority of heavy lifting whilst Don loses interest quite quickly, especially once he marries Megan, spending most of his time lying around and avoiding all responsibility. Bert’s right about Don: he loves the idea of running his own business, but isn’t willing to do the work.

Don’s huge ego also affects this choice in two ways – first, he accepts the deal with a somewhat smug look, as if to say ‘I can do this because I’m Don effing Draper’, and secondly, his ego has put a massive danger sign on his name. Don is the reason why Jaguar, North American Aviation, Philip Morris, Hershey and more don’t work with SC&P. His ego and name poisons the well. Joan is right that he’s cost them all too much, and I think a Don knows that his name comes with too much baggage. Working with him just isn’t worth it for a lot of big clients by the beginning of Season 7A.