I'm +1 on this. Ignoring the semantics of whatever the flag is or future plans to try and provide a fully statically linked binary, from a server app deployment point of view this makes sense.
Statically linking the (Swift) standard libraries makes deployment easier as you don't need to dig around and ensure that you copy over the different libraries. This not only simplifies deployment/build scripts for things like Lambda and Docker, it should also speed up cold start times on Lambda etc.
For 99% of cases where most people are deploying a single binary onto a system this makes sense. For those that need dynamic linking (e.g. those with multiple binaries in a system) as long as they can turn it off it should be fine. Making the default better for the majority where those in the minority have the option to opt out makes sense 