Because his intro comic was this awesome cover:
And because it was the first issue of Walt Simonson taking over the book, and his artwork was fucking incredible and awe-inspiring, compared to the bland stuff that came before. The first few fucking pages were this:
I was totally blown away by this issue when I picked it up, and Beta Ray Bill was, as mentioned the first being I was ever aware of to be "worthy" of picking up Mjolnir. Also, he was just awesome. He was already almost a match for Thor, and then he picked up the hammer and had Thor's power *added* to his.
Yeah, he has one of the dumbest names ever, and he looks funky. He's still awesome despite all that. There are some pretty good limited series and such with him too, aside from this main Thor storyline, which coincidentally also dealt with Surtur (spoiler alert, he's the one doing the forging).
And when he gets his own hammer, we get this fucking page!