Remember when Stands could fucking kill you if you weren't mentally strong enough to use it? What ever happened to that...

How did B.I.G. know that dying would activate his Stand?

It didn't.
He was capable of manifesting it on his own and who knows what a controlled version of it would have even done.
His hatred was so great it allowed the stand to live on in his stead and now it's a pending existential crisis unless pucci resetting the world made it go away.

To be fair, it's not the first instance of a stand outliving its user living independently. Anubis and the electrical tower stand come to mind.

Then there's Kira's dad's ghost, which was... well just weird. Bizarre even.

classic jojo shit writing

A tree and a gucci bag

Wasn't the tree the stand user, not the street?
Also you forgot Joshu

Its based on her soul, which looking at her life means holly likely has mental issues from being a spoiled new yorker.

The radio tower had a user

you forgot Polnareff

Pol when he was young