The current thread on the A12 reminded me of this.
When I was young, it always struck me as rather strange that the trunk road from London to Norwich struck out boldly across relatively unpopulated country, rather than following what would seem the obvious route via the A12 and A140 through Chelmsford, Colchester and Ipswich, which is also followed by the main-line railway.
I'm going to disagree with you here: the A12 picks up larger settlements, but there's nothing of any size on the A140 at all unless you make the detour into Diss. The A11 has a much more regular pattern of towns (Epping, Stortford, Saffron Walden, Newmarket, Mildenhall, Thetford, Attleborough and Wyndham) so makes a lot more sense for a coaching route and early motoring route to Norwich.
The fact the main railway goes that way is largely historical accident: rivals tried to build a western route via Newmarket or Cambridge, but got bogged down in politics. Even on what we ended up with, you could run a reasonable service via Ely, and I think pre-unification there was one.