It's also a saturated market because of the low barrier of entry, without an advertising budget you are taking a gamble no matter how good the gameplay is.
A whale is someone that spends a tremendous amount of money on mobile games. These are the people most games pander to or otherwise design themselves around
Low barrier to entry if you're not counting visibility. Yeah you can publish to the stores, but nobody will see it unless you are ordained by the gods at Apple and Google, or you buy eyeballs (and have the capital to do so.)