Premade cake mix is astoundingly and incomprehensibly moist/tender compared to anything you could come up with on your own. Hundreds of food scientists who get paid tens of millions of dollars a year and who have collectively put in at least a hundred thousand man-hours into formulating the absolute best possible cake mix with ingredients and processes you could never even dream of replicating in your home kitchen.

It's okay that yours isn't as good. It literally can't be. Homemade cakes are just different than boxed ones and there's nothing you can do about it. That's just the way it is. But don't get all pissy because you're too much of a brainlet to understand why boxed cake mixes are as good as they are.