I also don't understand why use a flood as the mechanic. It seems unnecessary to punish all the animals for something humans did. Since all humans were to be killed except one already faithful, there's no need to hide. Why not God just make everybody fall down dead instantly. Or make them vanish.
Christians just seem to lack imagination regarding what an omnipotent force can do.
The flood only makes sense if we think that it's a natural phenomena that actually happened and was later mythologised, and of course exaggerated.
That's the point of mythology. If we see it this way there's no need to posit a God that actually exists.
If I were God during the Flood times, I'd have had everyone die in cool and interesting ways, like in the
Final Destination movies.
Then people's last thoughts would be like:
"Whoa! That dude just got beheaded by a shovel which fell out of a window after the lady up there was kicking around as she tripped and got strangled by her clothing line. I'll give it an 8 out of 10. Oh look, I'm about to be beaten to death by a gorilla who escaped from the zoo wagon that crashed after the wheel broke and flung the driver into the display window of the knife store ... this should be entertaining for the next guy to watch".
Add a bit of flair to the whole genocide thing.
Since God's omnipotent, it would take him no more time and energy to think up an original and exciting death for each individual person as it would for him to have one generic event kill all of them.