For one, I'm not sure I'd want any more Five Eyes entities running
Exit nodes. Most embassies are already a haven for espionage activity.
You'd pretty much have to assume they'd be sniffing the exit traffic.
I doubt Five Eyes countries embassies would bother running tor since they have budgets to easily encrypt and funnel all their traffic back to their home countries.
If anyone would be running tor nodes, I would imagine it would be countries w/ smaller budgets who would be looking for more cost effective ways to make their traffic hard to sniff.