Why can’t I buy left for dead on my Xbox X

Because it was delisted a while ago. It's no longer possible to purchase digitally.

It says that it is currently not available even if I change my location to a different location

To add to what Smwutches said:

If you are changing your location to somewhere you dont physically live you are actually breaking the rules so id stop doing that if i were you.

I'm having the same problem but I can't download crisis, or left for dead 2. I tried deleting caches, deleted the failed game from the hard drive, restarted the x box downloaded my profile again, checked my settings, tested my connection. I can download
the demo for left for dead 2 but not the game I will let you know if I find the answer. oh and I got charged on my card for the items I was even able to buy points with my card. idk

some games might not be available in all region stores. I don't know if it's the case of Australia. try these links and see if you can buy them https://www.microsoft.com/en-au/p/left-4-dead/bphf60shqfxn?activetab=pivotverviewtab
https://www.microsoft.com/en-au/p/left-4-dead-2/bwvzhjn0g3c3?activetab=pivot:overviewtab If they are available, you'll
be able to play them on your australian xbox one x; and since you are in the australian xbox store you'll pay in $AUD.

Hello @ramonava939!

Left 4 Dead and Left 4 Dead 2 are both currently available on Xbox One.

Buy Left 4 Dead - Microsoft Store

Buy Left 4 Dead 2 - Microsoft Store