Less experienced players often seem to be performing for the other musicians, showing off what they know, playing difficult stuff and playing it fast. They don't notice if anyone else is joining in. More experienced players, while definitely trying to play their best, also work to fit in - for example, they try to make sure they're playing in rhythm with everyone in the room. They'll play quietly at times and leave space so others (especially singers) can be heard. They may play very simply to help others follow, or choose simple tunes so that more people can participate.
My first jazz music teacher used to say that music was like a conversation. I see more and more ways that he was right.