Isn't there ever a time when we see this lingering, our W's give us many signs that they WANT to come back, that we need to jump in and pull them out?

That assumes that you have control over the WASs' actions. All you can do is give them, by your consistent actions, reasons to reconsider. In effect, that can have a "pull". I think it's cumulative, not any one single act is going to have a WAS jump back, though one may eventually hear their WAS say something like, "but it was when you did [whatever] that I realized I loved you"... yet, in fact, it was not that one act, but all that came before that set the groundwork.

but here we are weeks, months, years, living with something that maybe could have ended long ago should we have stood up to it and demanded that it end.

The problem is that the risk of making such an ultimatum outweighs the pro, especially if the ultimatum is made at the wrong time, such as when the WAS very much wants nothing more than not to be in the relationship.

If it takes months or years, the trade off is that the WAS did have time then to discover if their actions paid off with the grass being greener or not, and self-realizations can set in that lead the WAS to figure things out.

I think in the end, we hope for a stronger union then would be possible if we forced them back into an unhappy R with us, unchanged and still looking outward for happiness. Sound about right?

And that's another risk to ultimatums, should the spouse respond to the ultimatum and come back for any other reason than real love and determination to make it work.