A common misconception is that employers always reward good work. Unfortunately, asking for a raise isn’t as simple as, “I’ve done X and Y, so I think I deserve a raise.” When you put it like that, you will likely hear an excuse like, “there is no budget.”
More importantly, asking for a raise makes most of us feel uncomfortable. How do you even ask the question? How do you prepare? What do you do when your boss says no?