I tried in 2017 writing it in rust and found some compiler bugs. I also found compiler bugs in c++ tho to be honest, but I felt more comfortable in c++ so decided to write the first version of it in c++. The huge advantage is that storage engines in particular need to be more conservative in many dimensions and having seen success with scylla, seastar was apealing to me as a 'tried and tested' for storage systems.
Prior systems I had built with facebook folly (c++ lib) and had also written my own eventing systems in the past, but the real value is having seastar being battle tested since 2016. Largely it has been the right decision for us as redpanda for it's young age has benefited from the stability of seastar.
I'm not necessarily advocating it [1] but the parent's claim was that those programs could benefit from memory safety, thread safety and better concurrency and C++ does not deliver along that axis.
