I'm referring to the visual style, the content, the markup, and ... well just about everything about that page...
* Things like wasting so much space on the oversized title.
* The term "modern" has become a euphemism for "limited features and a crap interface".
* Their feature descriptions are simply terrible. The word "sky" doesn't end in e.
* The poorly chosen generated artwork they've used.
* Behind the scenes, the markup is an ugly mess - they use CSS classes as if they were inline styles.
* etc
Others might not see some of those as issues, but it's their combination along with many other individually minor things which collectively say "this is shit".
> I'm asking because I am trying to figure out why it would have been selected in the first place, other than it is free.
People are attracted to things that are familiar, so the more people have used similar "modern" software in the past, the more crap like Flarum will appeal to them.
> BTW, the Wikipedia page is way out of date. I don't know if forums will make a comeback, but if they do - Beehive should be the first and last stop.
A double-edged benefit/drawback of Wikipedia is that they don't like people too connected to a subject to write about it - in some ways we should be happy that the Beehive article still exists at all; a lot of other Open Source software articles I previously tried to create haven't survived.
To get a better article (and more attention/use in general) would need reviews in credible tech websites, and they generally need a reason to write about a topic in the first place.