Encoding is definitely in Wuffs' long term objectives (it's issue #2 and literally in its doc/roadmap.md file). It's just that decoding has been a higher priority. It's also a simpler problem. There's often only one valid decoding for any given input.

Decoding takes a compressed image file as input, which have complicated formats. Roughly speaking, encoding just takes a width x height x 4 pixel buffer, with very regular structure. It's much easier to hide something malicious in a complicated format.

Higher priority means that, when deciding whether to work on a Wuffs PNG encoder or a Wuffs JPEG decoder next, when neither existed at the time, I chose to have more decoders.

(I work at Google, and am the Wuffs author, but have nothing to do with Jpegli. Google is indeed a big company.)

Thanks for the answer!

The first paragraph in Wuffs's README explicitly states that it's good for both encoding and decoding?

No, it states that wrangling _can be_ encoding. It does not in any way state that Wuffs is actually _good_ for it at the current stage, and I do not know of any nontrivial encoder built with Wuffs, ever. (In contrast, there are 18 example decoders included with Wuffs. I assume you don't count the checksum functions as encoding.)