I guess because it's off topic. TFA is about a specific Rust issue and a generic comment about "Rust is hard to learn" doesn't add anything to the conversation. It's like the generic "C++ is way to complicated" comment under every C++ post. They just incite language flame wars and district from the actually interesting stuff.
It's because, for some reason, the rust community is extremely, overly aggressive about downvoting. I think we can all just admit that - I've been using Rust since 2014 and it's always been an issue and it needs to be called out.
I haven't commented/been upvoted enough to be allowed to downvote, and it is honestly quite liberating and lets me focus on elevating what I think are positive contributions.