There are a couple of things at play here.
1) Your CNS isn't used to moving that kind of weight anymore. It needs to be retrained too.
2) Your muscles have gotten weaker. The cool part here is that they were stronger at one time, so if we were to be able to chart your progression back up, the line would be much more steep.
3) I believe in a theory I like to call "strength consolidation." Essentially, I argue that the longer you lift at a certain weight level the more accustomed your body is at dealing with it. This in turn makes things like recovery from an injury faster or jumps to a higher weight easier. Think of it like this. Lest say you just started benching 225 and you decide to give 250 a try. If you haven't built a solid foundation with 225 your body is going to freak out and say "hey, what the hell? I just learned to bench 225, what the hell is going on?" Or to put it another way, its sort of like teaching a kid one day to multiply fractions, then the next day expecting them to multiply matrices. The kid doesn't have the math foundation yet to make that jump.
So, the short story here is, a lot of what you can expect comes from how long you trained at the weight you were at prior to the injury, how bad the injury was, and what kind of layoff you had to have.
The good news is it will all come back sooner than it took you to get there in the first place.
B-