Why are Server Actions not executing concurrently?

Consider the following functions:

async function printAB() {
  console.log("A");
  await new Promise((resolve) => setTimeout(resolve, 1000));
  console.log("B");
}

async function f() {
  printAB();
  printAB();
}

the usual expected output of f() would be

A
A
B
B

as the console.log('A') statements can execute concurrently with the timeouts. Indeed, this is what we get if the functions are either both on the server (actions or defined in a server component) or both on the client. However, if printAB is a server action, and f is a function in a user component, we get

A
B
A
B

. Why does this happen? This behavior could cause lower performance if we use multiple actions at once, is there a way to avoid it?

from Why are Server Actions not executing concurrently?