Bleeding Cool previously reported that CBR chose not to ask Harley Quinn writer Sam Humphries about the absence of Poison Ivy in the Harley Quinn comic since he took over writing the title. Especially with her currently-expressed crush on Booster Gold. But when Humphries was doing a Live Video Chat, that seemed to be what a few people wanted to ask him, he was more than happy to talk about the issue.
Humphries says that he would love to write a story with Harley and Ivy together but DC is a shared universe, that means you don't always get to use the characters you want to use, they're not always available or there's other things are going on. No Ivy right now… but they are hanging out in every episode of Harley the animated series right now. He continued to answer, saying "I did not write Ivy out of Harley's life, you don't always get to use the characters you want to use. I'd love to use Ivy but it's not on the cards right now. It's not always up to us who we get to use in our books."
It has been noted that there seems to have been an editorial stance to a) make Poison Ivy a bad guy again and b) remove her as ever having been part of a couple with Harley Quinn, as previously established in the Harley Quinn series and in Heroes In Crisis. Plenty of her fans aren't entirely down with that, after seeing a more nuanced Ivy in the comics in recent years, though that portrayal has been spotty of late. They also see the removal of her from Harley's life as another example of straightwashing Harley Quinn now that the character has a higher media profile.
If Sam Humphries is not allowed to use Poison Ivy in Harley Quinn, it does seem to fit into such an editorial edict. Bleeding Cool will continue to look into the current situation with some rather interesting sources starting to talk. Of course, if you have your own observation to share, please do.