Because noah's arik is scientifically impossible.
At best someone named Noah had a boat during a local storm and gathered his goats, dog, chickens, etc. from his farm and sailed off 'till the flood went down. The locals that survived the flood then passed on the story from generation to generation, each time growing bigger and bigger until it became a world flood and not just his farm animals but every animal.
Sorry comrade, there is absolutely no way there could ever be a boat that could fit 2 of every species on it. It is scientifically and logically impossible.