That's just not true. The inbound rate on Toll-free is almost always higher than outbound termination. Only in rare, high-volume circumstances is Toll-Free inbound cheaper than outbound.
Usability is a huge issue, but I think that it comes back to the bottom line cost figure. The usability is just one of those problems that no one wants to start to deal with because of the cost. If outbound was cheaper someone would've found a way to do it (IMHO).
You may want to re-read your comment. If Toll-free inbound is higher than outbound, then why wouldn't they do outbound more often? We're talking about (in many cases) businesses like banks which offer toll free numbers. So obviously cost is not the dominating factor here.
Some systems did implement outbound calling for increased security. I'm thinking dial-up (BBS/remote access) scenarios. Windows NT, for instance, allowed you to allow a user-defined or preset callback number. Although, for user-defined, its more likely a cost issue than security.
Usability is a huge issue, but I think that it comes back to the bottom line cost figure. The usability is just one of those problems that no one wants to start to deal with because of the cost. If outbound was cheaper someone would've found a way to do it (IMHO).