Why are CA root certificates all SHA-1 signed (since SHA-1 is deprecated)?

I understand that SSL certs cannot be signed using SHA-1 anymore. Yet, all CA root certificates are SHA-1 signed (mostly). Does it mean the same algorithm that is no longer trusted for "you grandma SSL shop" is fine for the uttermost top secured certificate of the world?

Am I missing something? (key usage? key size?)

Solution 1:

The signature of the root CA certificates do not matter at all, since there is no need to verify them. They are all self-signed.

If you trust a root CA certificate, there’s no need to verify its signature. If you don’t trust it, its signature is worthless for you.

Edit: there are some very relevant comments below. I don’t feel comfortable copying or rephrasing them and taking credit for them instead of their authors. But I welcome people to add explanations to this answer.

Solution 2:

At the end of the day, a root certificate is self-signed. It is never signed by another entity except itself. The root certificate gets its trust through out-of-band processes like submitting it to a browsers list of trusted publishers, or getting it accepted by Microsoft for insertion into the default list of Windows trusted publishers.

These certificates (and the companies that self-signed them) are (allegedly, hopefully) thoroughly vetted through other means than just their signatures.