This would be different if you are in a subreddit for a niche topic, sure. But there are higher chances of creating healthy online interactions in Forums than a subreddit. You meet with regulars more often. Knowledge transfer is better cos you know the skill levels of different people based on your interactions and experiences. This is opposite cos in a subreddit depending on the topic. There is a high amount of irregular folks. This means you have no idea how to rate the interactions than to take them on face value. These are all small but important things that are important when it comes to a community.
Think of forums like your neighborhood. You participate and nurture it. You know most of them and the rate of new people are less than you can catch up with the pace among other things.
PS: These are some of my thoughts, people have different ideas and opinions on forums.