Who needs the damn things?

Think of it as 'planned obsolesence', but with guns

As for my family and I we'll keep our sporting, hunting and life saving firearms.

which I think is bullshit, but it is their property. They can do what they want.
The photo shows stacks of rifles and shotguns that doesn't look like they were well cared for.
As for why, I don't know. Maybe his twin sister is a cat lady?

There's always an "opportunity cost" to this kind of virtue signaling.

The heirs may feel all warm and fuzzy, but that money could easily be converted by an auction into food and shelter for the homeless, education for children that need help, or any number of good works, then they might have a reason to feel smug and self satisfied.

Destroying them will just give them a short term high and not save a single life.

Beretta, Savage, Glock, SIG Sauer, and Colt thank them and encourage other owners of similar durable goods to follow suit.

All that value going to waste.
If the family does not want to deal with the sales, find an FFL that does consignment sales. That gets you the background checks.
Just selling all that ammo would make a tidy sum.