Imagination gets swamped by the flood of the other.
But when flirting online, fantasies run free because the experience of the other is comparatively unconstrained by who they are.
All identifying information has been removed or disguised and all permissions have been secured.) Consider a professional 43 year old divorced woman who started dating after the end of a 15 year marriage. She told me she "gave good profile" and "gave good message,” and loved doing so.
She would invest these men, or rather their online presentation, with all the qualities and feelings she wanted them to have and then experience those qualities as coming from them, not her.
Their role was not to get in the way with discordant responses—and if they did, watch out, they might then have to meet in person. She felt their notes and messages were pleasure-filled discoveries.
In contrast, in-person flirting is a wide open channel.
Meeting in person, though promising all the pleasures life can offer, also makes unavoidable the mysterious puzzles, needs to avoid or possess, and too-muchness of body-to-body sexual enjoyment.
And some want to stay on because online is the only place they can get what they want.