Ah but he IS interested. There were two episodes that really showcased how interested he is. One was where a hockey player was killed during a game. Sara and Grissom were sitting alone in the bleachers and he said he didn't like hockey, she said why? He said, baseball is more my game. All those stats and numbers, it's beautiful. She said, since when do you care about beauty? He said, since I met you.
Then there was the guy about the same age as Grissom who they suspected murdered a young girl that slept with him (and many others). Grissom had this long speech about it in the interrogation room. He basically said, you and me are a lot alike. We both made our career our lives and then we get old and turn around and realize that we're missing something. And someone comes into our life that we could be with but we have to make the decision to let go of our work to have her. You did what I couldn't do. And when she cheated on you, you couldn't handle it.
...cut away to Sara with a pained look on her face who heard the whole thing from behind the double sided mirror...
He basically told her (in very few words) that he can't jeopardize their jobs for a possible relationship. But the blond chick no longer works with them. And he's got a thing for blondes; he screwed up his chance with the bone specialist already. I don't think he'll make the same mistake again.
As for ER, they jumped the shark for me when Lucy and Carter were stabbed and Carter became a druggie. I use to watch it religiously but don't anymore. Did you know Sara Sidle used to be on ER? So was someone else from CSI, can't remember who.