You need healthcare, you need an emergency fund, you need elder care, retirement. College fund for your kids. if you get hit by a freak meteor and become mentally/physically disabled, you're not going to be able to make $25k/yr.

For it to be FUM is enough to live off the interest at 4% withdrawal for the rest of your life. At an estimate, it takes between $250k and million dollars to get through a case of cancer. You're not getting through it on $25k/yr after you get fired because you can't work because you have cancer, and you won't be able to afford lawers to fight getting fired either.

$25k might be enough for a twenty year old with no responsibilities who can still eat dollar store ramen, but it's not enough for someone with responsibilities past subsistence eating.

Also don't forget inflation.