I aint just xbox "fanatics" bro. None of my large group of friends IRL are xbox "fanatics." Most of them don't even own an xbox and they still feel there is a slight bias.
Could they be just picking up on what others have mentioned where it just seems that way because PS4 is the most powerful right now and the majority favorite? Yup. But that's how it seems so that's what people are going to think. Even if they are wrong. This doesn't just come from xbox "fanatics."
I do think there's a bias, but one that the company themselves caused.
MS this gen was all tight lipped, we are going to talk about this very important subject when we feel like it, and even for their games they hold on too much to have e3 blown out of gameplay for instance.
Whereas Sony is always feeding the press with previews and their fans too. Look for example on how sony handled Horizon, and how Ms handled State of Decay 2. Even though it got delayed Sony showcased Horizon a lot, made tons of trailers and preview events. Ms announced SoD2 went radio silence other than assuring the game comes out this year.
So bias is simply a reflection from that. Every time they showcase a game on them generate clicks so the press loves Sony. The fans see the game getting promoted and become hyped too.
Now other than that there's definitely a sentiment of entitlement sometimes but most of it it's just a reflection of how both companies are handling their market.