The distributors don't want another IPA or pale ale, or what some would call "normal beer"
The distributors are beholden to/controlled by Big Beer. One implication of the situation described in this oft quoted and still excellent articlehttps://www.goodbeerhunting.com/blog/2017/5/5/watch-the-hands-not-the-cards-the-magic-of-megabrew
is that Big Beer doesn't want these for good reason:
They want to control or influence a sufficient segment of what is popularly perceived as definitive, quality "craft" so as to bring its perceived quality (indicated by price point) into relative parity with their core brands, so as to in turn enhance the perceived quality, and hence the actual brand equity, of those mass market brands. They want to keep independent craft confined to increasingly narrow niches. Of course they don't want more competition in "normal beer" (I'm just going to use this convenient shorthand you've provided, dzlater.)
It seems to me they are missing a huge opportunity. While craft, in a very limited niche (or niches,) holds fast -- even growing in certain statistical manipulations like number of brands or dollar sales, but not in actual number of loyal consumers -- beer sales as a whole continue to decline, while wine and spirits and malternatives grow. I believe this is because the potential growth market in beer is would-be consumers of "normal beer," but not being served, they turn to other adult beverages. Big Beer doesn't care, they will just invest in those sectors. (So too increasingly the likes of Boston/DFH.) Note also that one of the first effects of consolidation of ownership internationally was the disappearance of most of the former imports which might have filled the middle ground between the ephemeral avant garde of craft and the gas station 30 pack. Again, Big Beer just sees this as a case of well, we have a brand presence in that market, no need to keep shipping stuff across the ocean.
It seems once again that the 3 tier system, intended to protect the consumer from undue influence on the part of brewers, in fact now insulates the brewer from the inconvenient influence of consumer demand.
[EDIT for typo]