Facebook may be evil but I don't think they're anywhere near "inject malware into global supply chains to push adoption of a public engineering side project that they don't directly profit from and most executives don't care about" level of evil. Is it possible? Sure anything is possible, but that is wildly beyond many many more plausible explanations and there's zero evidence leading us down this path. And why would they go through the trouble of backdooring zstd, which has a highly observed codebase, when they just successfully backdoored lzma because it didn't have a lot of maintainers?

While it's true that zstd is commonly favored for having "good" compression at blazingly fast speeds, which is useful on the web and on servers, Zstd 's max compression setting (zstd --long -19) is actually within about 5% of LZMA's but faster, so it replaces most use cases of LZMA except when that extra 5% (and that's not even constant; some inputs are even better on zstd) really does matter at all speed cost