Why isn't Leo compatible with Aries and Sagittarius when all the three are fire signs?

I have noticed this in many people.Aries and Sagittarius are made for each other.They are highly compatible.But Leos find it difficult to get along with Aries and Sagg.I am an Aries and I am not fond of Leo.In my experience Leos have serious attitude problems.They are of average intelligence and average talents.But they try to show off and pretend as if they are great people.They also disparage others' abilities just to make themselves look better.In my opinion this is not a good practice and thats why I don't like them.