Why did it die?

Here's the details... no hidden occurrences,

I purchased a 2015 MacBook 12" Retina for a trip to Asia. I was traveling extensively via Plane, Train and Boat so I wanted something compact.

It arrived used from eBay, but working perfectly.

I was in and around China for 1 month and had absolutely zero issues with the unit.

I arrived back in the states and still, zero issues.

I was leaving for NY for a few days and placed the MacBook on my kitchen table, plugged in to charge.

After arriving home I unplugged the unit and attempted to turn it on and nothing. No bleeps, bings or flashes... absolutely nothing.

I believed it may have been improperly plugged in so I left it to charge again... nothing. Changed charger and cord... nothing.

Something was obviously wrong and all Apple Support Documents say remove the battery. So, I opened the unit and displaced the battery from the logic board. No luck.

I replaced the KeyBoard Ribbon Cable, USB-C Port and even a new Battery... nothing.

So my question is, what happened? How does a unit go bad just sitting on a kitchen table?

Before any rants - I live alone, so no my kids didn't spill anything on it nor did anyone touch it while I was away. I tried all the SMC and PRAM reset methods too. Nothing works.

Please Help.