Elyoukey, no worries, I had spotted the distinction.
Why play Tutatis or learn it when you already play and enjoy BB? Tough question really, being a Blood Bowl fanatic for the last decade and not having finished reading the Tutatis rules yet, i'm probably not best placed to say though i'll give my thoughts on what I find interesting on a purely face value front.
Size and scale, Tutatis is a lot smaller than anything else out there other than travel BB. This makes it even more portable than Blood Bowl.
Models, the Tutatis models are lovely and being 10mm scale have to have a strong distinctive style to stand out. In this case it is a fairly cartoonish style rather than the harsh bb style.
Imagination, while Orcs and Dwarves are fantasy staples and hard to avoid teams like the Poffy team are awesomely unique.
Mercenaries, while in bb the stars are just souped up versions of players showcased elsewhere Tutatis has a range of players who have their own specific special rules (and who doesn't like a player who can eat the ball

).
Rules, now I've not read all of these but as Gaelic Football seems to very different to American Football I can only imagine that games based on them will be very different mechanically, although being a dice based game there's always that similarity.
I suppose the primary reason to give Tutatis a go is the same as when trying any new game, because trying it might give you another source of pleasure.
