If you decide to trust "the Python Foundation", what does this key do for you if you're already downloading binaries from python.org? And if you don't, how much does the fact that they have a key help you? Anyone can get a key.
Hackers can compromise python.org and sign stuff with a key advertised there. But the site is just one point. It's much harder to hack python.org and also their GitHub and Twitter account (and DNS and dozens of other supported services).
Keyoxide makes the signing key links on multiple sites thus raising a bar for accepting fake key. It's not a silver bullet obviously. Just makes the attack harder to pull and is machine readable (instead of making humans check the keys).