If Gin ate it he'd just shit Aizen out eventually, more powerful than ever
Gin-"I put a poisonous shard in your heart",
Aizen response-
"Now you know Gin assuming will get you no were (snickering), who even say I need a heart to live"? I'm immortal in the beginning, and unfortunaltey for you to the end, just as I always planned!
"The End Justify The Means"