In 2003 no one would have been asking any of these questions. Yes, Dave's a high profile member of the Beach Boys now, but that wasn't the case for the majority of the past 48 years.
Not sure that's *quite* accurate. The renewed interest in David really came when he rejoined the band in the late 90s, although at first he was regarded as a bit of a joke until enough people had seen him perform and then later Jon's book came out. Your general point does hold though, of course.
And of course for a long time David wasn't particularly interested in the Beach Boys' music either. I remember reading an interview with him from the early 80s where he absolutely slated pretty much everything they'd done and Carl Wilson's guitar technique in particular, saying they hadn't progressed at all since he'd left.
I don't see it as particularly odd that they had relatively little contact for a few decades though -- when David left the band he was 14 or so. I can't think of a single friend from my early teens that I spend any time with.