I've seen "better designed" open source pages, but they tend to send the wrong message. When you see a mostly-well-designed open source page, your brain just feels like you're being tricked. You feel like someone's trying to charge you for something, or it just feels wrong.
Design is contextual, and what we think of as "well-designed" tends to be from a SaaS perspective, and that sends the wrong message. You see it and think "oh, this is a SaaS product," and your brain just feels weird.
This is true for all design. In markets, generic brands use a worse design to signal they're "cheaper," cereals for kids use cartoons, etc. The vibe needs to match the product, or else your brain sets off alarm bells.
Open Source projects use design to project what they value. Org mode for Emacs should feel like... a site for emacs. Simple, clear, no frills. Whereas a site like Prettier looks nicer, because that's the whole point.
(Also, separate "design" from "usability"... this site isn't pretty, but I can find everything I need super easily!)