There is some logic here, having a business relationship with a party that now has a contractual duty to you, is a stronger guarantee than an open source project.

For instance Windows is source available, to many businesses, so in one sense it’s open source, and the other sense is closed source. From a business perspective that’s a reasonable trade-off sometimes

I recently learned that my company prefers closed-source tools for privacy and security.

I will suggest that same logic to my banker too: a vault whose key they won’t own, but I will. Don’t worry, all your money will be safe with me, it’s a promise 😇