zsh/bash string to array not working using parentheses

Do you know why the following is not converting string into array?

  STR="one two three"
  array=("$STR")

  echo "${array[@]}" # prints: one two three
  echo "len: ${#array[@]}" # prints: len: 1

>Solution :

cat "73276948.sh"
#!/bin/bash
STR="one two three"
array=($STR)
echo "${array[@]}"              # prints: one two three
echo "len:      ${#array[@]}"   # prints: len: 1
echo "1ST:      ${array[0]}"            # prints: one two three
echo "2ND:      ${array[1]}"            # prints: one two three
echo "3RD:      ${array[2]}"            # prints: one two three
echo "Using loop:"
for (( indx = 0; indx < ${#array[@]}; indx++ ))
do
        echo "$indx" "${array[indx]}"
done

Output:

$ ./73276948.sh
one two three
len:    3
1ST:    one
2ND:    two
3RD:    three
Using loop:
0 one
1 two
2 three

Related difference:

array=("$STR")

array=($STR)