I'm one of them, so please just believe me instead of trying to correct me ;) It's an ongoing problem the project talks about that there aren't enough newcomers ready to write more SIMD code with good enough quality.
> Should they be showering ffmpeg et al. with praise or something?
The top reply is "just do this other thing that the article said was unworkable", so not doing that would be a start. Though, the article could've spent some more time explaining why intrinsics don't work well enough.
> but hardly anyone else can justify doing that
Other people mostly only target one CPU architecture as they're less important, but they also get paid and ffmpeg developers largely didn't. (These days more of them do, but those people are contributing security work more than performance work I think.)
It's similar to how x264 was better than every commercial competitor while working for free, simply because they took more time to think about what they were doing.