[johannes1234321]

> Doesn't that undermine the whole decentralized web of trust concept? All those services are operated by US companies - or what if someone simply compromised Keybase itself?

Ideally: Nothing. Keybase refers to other sources. I.e. a page on GitHub woth username and key fingerprint. So if keybase is compromises those links miss and it's no prove.

[revi]

In reality some people stores their private keys there ('encrypted' according to them) so it can be stolen when they're compromised.