As Complaintdesk above so well wrote, gates do need a roof above them in order to avoid rotting or rusting, depending on if said gates are wooden or made in metal.

However, making use of stone blocks above the gates do have the same protecting effect against the weather.

You will find damage to wooden structures inside your lodge if you don't have adequate cover over it or the cover is too high above the tile. For example, if you make a smoke hole in your roof but don't cover it with a different angle roof or one of the roof caps the structures underneath (both horizontal and vertical) will take damage from weathering.

is it the weather? Are they wooden gates?

Is there a roof over them? Cause it could be weather damage. Have you ever seen them BELOW half health when you know nothing has attacked them?

I have a wall sconce outside on an angled beam that keeps becoming destroyed and I can never figure it out. Waves?? nope Thought it was not close enough to a bench, nope, extra walls from rando GD water attacks[not too likely], could never figure out why it would just deconstruct...so I don't put it up any more.

Wooden gates need to be covered by roofing pieces to protect them from rain/weather, because like all wooden building pieces they are susceptible to weathering damage over time.

https://steamcommunity.com/sharedfiles/filedetails/?id=2846603379

With one exception in that stakewall is not damaged by weather.

The angled beams are also not affected by weather.