It's not anything nefarious, just the natural blind spots of human reasoning. Titles are cheap. Your existing employer will always want to hand you more work,

It's not anything nefarious, just the natural blind spots of human reasoning. Titles are cheap. Your existing employer will always want to hand you more work, but not more money. If you are handling the work well, then the pain of not having that role filled is only a memory. Your future employer has an acute problem to solve and is already primed to spend money to solve it. The net result is that (current employer) is much more likely to increase your responsibilities/scope/title. While (future employer) will pay you. There are absolutely employers who will give significant raises to existing employees, but they are rare.