The expression ‘You can’t have your cake and eat it’.
What in the name of all that’s holy is the point of having cake if you can’t eat it? Cake is supposed to be eaten, it’s entire reason for being is to be eaten. Cakes can look beautiful but if they are inedible they are failure cakes.
If you have gone to the trouble of making or acquiring cake, it’s probably because you want to eat some damn cake. So why can’t you?
I’m assuming and it’s a big assumption that this saying is meant to convey that you can’t have everything you want. So maybe, ‘you can’t wear two pairs of shoes’ would express that meaning the same way.
Because if I have cake, I’m bloody well going to eat it!