Doesn't it make sense, though? It's a character that they've had to build from the ground up, whose perspective they've had to both invent and try to inhabit. When writing, they've had to filter events through that character's perspective. Considering how much time they've spent working on and thinking about them, why wouldn't it make sense for them to grow attached?
Re: I should just make a secret about this and I probably will, but...
Doesn't it make sense, though? It's a character that they've had to build from the ground up, whose perspective they've had to both invent and try to inhabit. When writing, they've had to filter events through that character's perspective. Considering how much time they've spent working on and thinking about them, why wouldn't it make sense for them to grow attached?