[lifthrasiir]

While that might well be one reason, it should be also noted that Zstandard optimizes for the decompression speed with a reasonable compression ratio while Brotli concentrates on the compression ratio at the slight expense of speed (though it is very hard to do a fair comparison). This is evident from their defaults, where zstd uses a fairly low level (3 out of -7..22) and Brotli uses the maximum level (11 out of 1..11). But both have the decompression speeds far exceeding 100 MB/s which is the practical limit for most Internet users, so zstd's higher decompression speed wouldn't matter much in the web context.