I think Reddit, like most U.S. web based companies aren't overly concerned with GDPR in many situations, and they are focused on what looks best for their IPO.
Firstly operating in the EU doesn't mean your entire global operation has to conform to EU regulations. Unless the user in question is in the EU, I think they would be hard pressed to apply fines.
But Reddit is a bit off the rails right now, I mean it is clear they aren't making good or smart choices, so even if this is solely bound to the confines of the EU, I don't think they are going to follow the rules, until they are made to.
If they don’t comply, they’ll get fined, and I have the feeling it will not be a small one given how they handle things