Breasts are made up of adipose tissue, which is just a fancy clinical term for fat cells. So why do men get all gaga over playing with fat?

Because they are there. Like why did the bear go over the mountain. Guys don't have them. They are fascinated by them and feel that playing with them makes a girl feel more like sex or at least sexual.

For the same reason (stereotype) of why women like men with a larger package.

They'd be more excited about that than a mans dad bod buddha belly

I don't know any men who go "ga ga" about breasts.  I'm not aware that "spare tires" have nipples.

Men play with butts .They hug and kiss butts because it gives erotic feelings .Same way they kiss boobs and suck the nipples .Even the woman is flat chested they can suck the nipples and play with the hidden area down .They can only feel and squeeze the waist which does not arouse any sexual feelings . Boobs and butts are two thrilling areas in love making .The fact that it is made out of fat cells is immaterial  . 

It's best not to question evolution and biology, my friend. It's confusing, but it exists for a reason.

Men liking women = possibly having sex with them = possibility of having children

That's about it, really. 

If breasts were only adipose tissue the surgeries to remove or reduce them wouldn't be so sophisticated. In reality they contain other physical elements as well. But men like them because "breasts are life" in the minds of breastfed infants and that attraction never goes away. 

Brain tissue is mostly fat and so are testicles.

its what you can do with them

Your knowledge of biology is laughably bad. Stop trying to be clever... it doesn't suit you. 

big boobs

chile