how can i stop a while loop background process without using kill?

i have a bash script with a while loop background processes how can i stop the while loop without kill the process so by set a STOP flag

Note: my script is works if i use kill but with stop flag didn't work

this is a demo of my script(using Kill):

#!/bin/bash


background_processes=()


trap ctrl_c INT
ctrl_c() {
    printf "\n[~] Killing background processes...\n"
    for pid in "${background_processes[@]}"
        do
          kill $pid > /dev/null 2>&1
        done

}

background_process() {
    while true
        do
         sleep 5
         printf "Hello World!\n"
        done

}

start() {

    for t in $(seq 1 10)
        do 
            background_process &
            background_processes+=(${!})
        done

    wait
}
printf "\n[I] Press 'ctrl+c' to kill background processes! \n"
start

This one works fine but the other method not work !

This is my same demo but with stop flag(not work!)

#!/bin/bash


STOP=0
threads=10
finished_threads=0

trap ctrl_c INT
ctrl_c() {
    printf "\n[~] Stopping background processes...\n"
    STOP=1
    # here i was checking that all the background processes is finish
    while true
        do
         if [[ $finished_threads == $threads ]]
             then
                break
         fi
        done
    printf "\n[+] Done\n"
 

}

background_process() {
    while true
        do
         sleep 5
         printf "Hello World!\n"
         if [[ $STOP = 1 ]]
             then
                ((finished_threads++))
                break
         fi
        done

}

start() {

    for t in $(seq 1 $threads)
        do 
            background_process &
        done

    wait
}
printf "\n[I] Press 'ctrl+c' to stop background processes! \n"
start

Can anyone tell me why this not works please ?

P.S: i am arabian btw so sorry if my English grammar is not good