I think basically it is more aggressive towards corrosion so if there is corrosion under the gold it can get under mined. Wheras, if you leave that corrosion alone, the gold on top remains conductive and it might be ductile enough to work in that state so long its on top of something
gold contacts are usually low current
I believe its kind of like chrome, where you get flakes. Imagine a microscopic flake thats 90% on copper and 10% on corrosion. It will stay intact. But if that corrosion under neath is removed, parts might fall off. Chrome is also incredibly resistant to corrosion, kind of like gold. Not as good, but its still a damn good metal.
Because the gold does not really decay. It just get displaced or grinded off by the contact. But it stays together like a concrete platform. So long its one piece and flat enough, the low current will have no problems going through there, regardless if some of it is supported underneath by oxide instead of metal.
Now if the oxides get undermined, you might have it try to 'fall into' the hole under neath from dissolved oxides (like if you sat on your bed and the middle was missing). This might get the bed sheet to get dislodged from around the mattress.
Thats my guess. There might be a different or additional reason
If you apply deoxit red to bad stuff, after 6 months you are left with some green crystals you can wipe away. Like petrified BNC connectors
I would just buy gold, because those switches will eventually cost you an arm and a leg if they go.....