Ronen's been flirting with him a lot on social media so maybe that's why? He's also been interacting with fans that are shipping TK and Buck. Maybe Oliver doesn't get that that's Ronen's thing yet. Ronen sees what the fans like when it comes to ships and he cashes in on it. He still calls Rafa Papi cause he knows it drives the fans wild. Oliver's the exact opposite way. He doesn't talk about any ships at all cause of all the drama that ensues. He says one wrong thing and fans will run with it and get their hopes up, then get mad when it doesn't follow through. Or attack him if he shoots something down. That's just about been how Buddie has been for him so I think he just wants to stay out of when it comes to anything relating to Buck and his sexuality.
Tuck is the next fan ship when it comes to the crossover and I've seen a lot of people talking about it and how Tarlos interacting with Buck will lead to Buddie being canon or whatever. However, Ronen and Oliver are doing a Q&A together for the crossover soon I think so maybe he'll follow back?