iOS GCD global queue priority both 0.5

I met the problem is why the following code print out priority is the same? Why is this? Thank you very much.

    print("main:\(Thread.current)")
    print("thread main priorities:\(Thread.current.threadPriority)")

    DispatchQueue.global(qos: .utility).async {
        print("utility:\(Thread.current)")
        print("thread utility priorities:\(Thread.current.threadPriority)")
    }

    DispatchQueue.global(qos: .background).async {
        print("background:\(Thread.current)")
        print("thread background priorities:\(Thread.current.threadPriority)")
    }

    DispatchQueue.global(qos: .userInteractive).async {
        print("userInteractive:\(Thread.current)")
        print("thread userInteractive priorities:\(Thread.current.threadPriority)")
    }

    DispatchQueue.global(qos: .userInitiated).async {
        print("userInitiated:\(Thread.current)")
        print("thread userInitiated priorities:\(Thread.current.threadPriority)")
    }

Log:

main:{number = 1, name = main} thread main priorities:0.5

userInteractive:{number = 3, name = (null)}

utility:{number = 5, name = (null)}

background:{number = 6, name = (null)}

thread userInteractive priorities:0.5

userInitiated:{number = 4, name = (null)}

thread utility priorities:0.5

thread background priorities:0.5

thread userInitiated priorities:0.5