No a lot of jitted code has pointers to addresses specific to that process which makes no sense in another process.

To make code shareable between processes takes effort and will have tradeoff in performance since it is not specialized to the process.

If the query plan where at least serializable which is more like a AST then at least that part could be reused and then maybe have jitted code in each processes cached in memory that the plan can reference by some key.

DB's like MSSQL avoid the problem because they run a single OS process with multiple threads instead. This is also why it can handle more connections easily since each connection is not a whole process.