He deserved it.
No, he didn't. Don't be ignorant.
While, without Bill Finger's contributions, Kane's original Batman would have sucked ass, without Kane creating a Bat-Man, Finger wouldn't have had anything to CONTRIBUTE to.
Without Kane getting the ball rolling, we wouldn't even know who Bill Finger is and he wouldn't have a legacy at all, unacknowledged or not. Bill also could have sued for the right to a byline, but he didn't, so in the end, he let himself get completely screwed on Batman. He never even tried to receive credit.
If Kane hadn't CREATED Batman in the first place, Bill couldn't have improved the character. So all of you think about that one before you get up on your high horse and lobby hate at a dead man who was worth more than you'll probably ever be. Bob Kane gets more hate lobbied at him than he is due. Fact. Bill Finger is martyrd more than is reasonable. Fact. The fact that Kane relented in later years and the fact that Finger didn't fight for his rights equal things out. You're not going to have everything handed to you. If Bill wanted credit, he should have fought for it.
Legally, there is no gray area, either. The character was already created and submitted to DC. Bill came to the table too late to get a creator's credit. Legally, Bill doesn't get to have a co-creator credit because Bob already created and submitted the character. All he did was make revisions after the fact. It's true that Bill shaped Batman prior to his debut, but the "right" to a co-creator credit is hazy at best. It can be argued that every non Bill Finger writer should get a co-creator credit as well, after all, they're all making revisions to the character after-the-fact, too. Just like Bill did.
Please understand that I am not anti-Finger. In fact, I think it'd be damn spiffy if he got the co-creator credit that he should technically get, even if legally, he's no more fit for it than Denny O'Neil, but let's keep things in perspective here. Both parties are equally guity of something. Kane for taking credit for what Bill did (up until the 80s), and Bill for just letting Bob do it to him.
Batman was created by Bob Kane. Fact. Kane's only crime was letting people attribute everything to him. Don't villify Kane more than is due. Not mentioning Bill Finger as a contributor for a few decades doesn't equal an evil plot to make Bill die penniless, which is how the "Raise the Finger" types act. Grow up and comprehend the truth.