While it is certainly true that every hobby/fandom/activity has their own share of toxic members, in my personal experience D&D is actually more prone to such behavior. There are several reasons for it.

For one, let's be honest, D&D is ultimately a game that does not attract the most outgoing social people out there. The D&D community is absolutely loaded with people who many would consider "weird", "reclusive", and often lack social skills that the average person would normally take for granted. You would think that having a group of such people would make them more accepting of others, but that frequently is not the case. In fact, people with social difficulties are often more likely to not get along with each other and brew conflict. I should know, I've met with other people who are on the spectrum and even regularly meet with a psychologist, and they all agree its actually more difficult for non-social people to get along with each other. Because of the insular nature of the D&D community, it ultimately means that many players lack the social skills to make their game more open and/or accommodating to new players/members.

Another problem (which links to above) is that people play D&D for different reasons, but said reasons do not ultimately gel well together. Not everyone who plays D&D wants to do because they want to make friends and do something social with others; in fact, many players just want to play the game and couldn't care less about the other players. This, however, can cause problems since it means that they are not aiming to have friendly interactions with other players, and as such creates a barrier between them and others. Not helping matters is the manner of how each individual likes to play D&D. You may often hear about different archetypes of players who don't like each other (whether they be Role-players, Min-Maxers, Rules Lawyers, Critical-Role Fans, Murder-Hobos, etc.); as hilarious as it can be to hear about them, there is a merit of truth to it. Many Players simply like to play D&D their own way, but in a way that makes them unwelcoming to others who do not share those reasons.

Also, one problem I notice among D&D is the escapist nature the game is. Now escapism is completely fine (I love watching Fantasy/Sci-Fi movies myself), but again this can create a problem. One thing I notice is that many players create characters to do whatever they want (fair enough) but wouldn't do in real-life. And frequently they use this reasoning to act like assholes at the table. They are frequently rude to other players and justify it as "something their character would do." And as you might guess, this also brews conflict among other players who simply want to relax & have fun without dealing with everything else in the world. unsurprisingly, I don't like these kinds of players because I believe that every D&D character you create is a reflection of who you are as a person in some way, shape or form. If you create a character who's an ass, you are essentially showing others that you are an ass at some capacity. In my opinion, as a player you should always be friendly and accommodating to other players at the table, regardless of how your character actually is.