> Why don't they make zstd images surely that would beat webp
zstd is a general-purpose compressor. By and large (and i'm unaware of any exceptions), specialized/format-specific compression (like png, wepb, etc.) will compress better than a general-purpose compressor because format-specific compressors can take advantage of quirks of the format which a general-purpose solution cannot. Also, format-specific ones are often lossy (or conditionally so), enabling them to trade lower fidelity for better compression, something a general-purpose compressor cannot do.
zstd is a general-purpose compressor. By and large (and i'm unaware of any exceptions), specialized/format-specific compression (like png, wepb, etc.) will compress better than a general-purpose compressor because format-specific compressors can take advantage of quirks of the format which a general-purpose solution cannot. Also, format-specific ones are often lossy (or conditionally so), enabling them to trade lower fidelity for better compression, something a general-purpose compressor cannot do.