The developer likes to shock his fans. Derek's betrayal will be a much more serious blow than Nick's betrayal, which no one cares about. Perhaps the most understandable motivation for the act would be that Derek doesn't like that MС is dating Maya. In episode 5, if Tremolo stays with Maya as friends, Derek happily welcomes him, but if they are in a free relationship, he gets upset. Derek probably doesn't think he's the right guy for Maya. By sending the video to Burke, he thinks to provoke a response from Burke and disappointment from Maya, but then it turns out that they broke up and Derek tries to make amends for the whole season 2. That's how I see it.