That's easy. The bulk of the broadcast audience wants to be entertained - and for most of them, trying to get them to rethink things - pretty much anything - doesn't qualify as "entertaining."
Frankly, even I don't want the radio color guy to be "trying to get me to rethink how I view baseball." That's not something that's likely to happen with little snippets of conversation between Franzke's PbP reporting - and a color guy talking over Scott's PbP to get me to "think," would be grounds for firing (or, I don't know, execution? 
).
My all-time favorite color guy was, and remains, Rich Ashburn. He was not an analytical color man - but he was the guy whose passing hit me harder than anyone else, excluding family, in my entire life.
And for the record, I'm not old-school. I'll happily digest analytical baseball writing; before the days of fangraphs, Baseball Prospectus, etc., etc., I bought Sporting News annual publications, and ran my own statistical analyses of prior-year data - in Excel, and before that using SAS or Minitab. But I don't want the color guy throwing out that kind of stuff (likely inaccurately) between pitches. Such a color guy would bring the appearance of authority to the subject, with no great likelihood of actually understanding or getting it right. Misinformation is far worse than no information - I think we've seen ample evidence of that in recent years.
