[snotrockets]

Redis actually has very few external dependencies compared to most modern FOSS:

IIRC, it only need libc and OpenSSL (the latter only if you build TLS) on your system, and provide their forked copies of Jemalloc, LUA, fpconv, HiRedis, Linenoise and Hdr_Histogram.

[nextaccountic]

those vendored dependencies are still libraries that redis couldn't use if those libraries weren't open source

for example, something like jemalloc is highly nontrivial