Why creating files in /dev/shm is not faster than creating files in /tmp?

Let's say I have two bash files. The first one is called diskFile.bash:

for i in {1..10000}
do
	file=$(mktemp)
	cat > $file  $file <<- "SIGN"
		"Hello World"
SIGN
done
echo "finished"

On Linux, files created inside /dev/shm are files inside the RAM memory of the system. But if I try executing the first file with time bash diskFile.bash, I get:

finished
15.56user 5.74system 0:20.25elapsed 105%CPU (0avgtext+0avgdata 6324maxresident)k

And with time bash ramFile.bash:

finished
15.20user 5.37system 0:19.45elapsed 105%CPU (0avgtext+0avgdata 6380maxresident)

The difference of time doesn't look like a significant one considering /dev/shm should be using RAM memory. Why creating temporary files inside /dev/shm is not faster than creating temporary files inside /tmp? Is there any way of speeding up the process of creating files using bash?