To be honest, it is because reddit still feels... frivolous? It doesn't have the toxicity that it did a couple years ago, nor the shallowness of its nothing-but-cat-pictures reputation. But neither is it a good platform for gaining customers or revenue. It is a place to gain traffic, but traffic without revenue is not the goal for most organizations. Now, if reddit traffic converted, I'd look deeper at it - but when traffic from reddit has conversion rates that are 25% that of the traffic from other social media? I just see no reason to engage any deeper.