While it's true that My Little Pony has had a following among furry fans for many years, it was a much smaller following than it was before Friendship is Magic came along. Different people like different things about shows that feature animal characters, and for some, the pre-G4 MLP had enough for them, while for many it was clearly lacking in areas where FiM succeeded. It just goes to show that anything featuring animals is going to attract the attention of at least a few furries, but you need things like good characterization and well-developed stories for it to become a major phenomenon in the furry fandom.
While it's true that My Little Pony has had a following among furry fans for many years, it was a much smaller following than it was before Friendship is Magic came along. Different people like different things about shows that feature animal characters, and for some, the pre-G4 MLP had enough for them, while for many it was clearly lacking in areas where FiM succeeded. It just goes to show that anything featuring animals is going to attract the attention of at least a few furries, but you need things like good characterization and well-developed stories for it to become a major phenomenon in the furry fandom.