Although many speakers look alike, there are very real differences. Studio monitors are designed to provide a flatter, un-boosted sound that carries over short distances. Rather than creating smooth and fully finished audio, they provide clear pitch and the true tone without speaker input or limitations.
With studio monitor speakers, sound engineers can hear each aspect of a recording clearly so that they can get the mix just right and find possible flaws to eliminate with music editing software. Studio speakers can also be used as inward-facing speakers for musicians while playing, allowing them to hear the other musicians and stay in tune.
While you may be tempted to only use over-ear headphones for a small home recording studio, having studio speakers can give you a much more complete sense of the sound you are recording. They are well worth the investment when you are producing your own music.