Why is the 360 store getting shutting down

because maintaining certification with credit card companies is expensive, and the 360 store no longer sells enough to support itself

You will still have access to all your existing purchases, and backwards compatible games will be available on the Xbox one and above store

They haven't shut down any regions store on the 360.

I'm in the U.K. & easily use the store on the xbox 360.

Considering you also need the xbox 360 store to buy backwards compatible games on a xbox one then why would they shut it down?

Zen is correct,your account,billing & actual location must all be the same.

Everything on the 360 store will be shut down once that marketplace shuts down.

The only thing that will change is that you will lose the ability to buy things you do not currently own on the Xbox 360 store. Accessing things you already own on all platforms remain exactly the same

Hi Krishna, my name is Rodrigo. I'm an Independent Advisor and a member of the Microsoft community and I'd love to assist you today.

The retro-compatiblegames available on the xbox.com store will still be purchasable.

https://www.xbox.com/games/store/

The games that are only available at the Marketplace Store from the Xbox 360 will not be purchasable.

https://marketplace.xbox.com/

I hope this helps.

Source:

https://support.xbox.com/help/xbox-360/store/xbox-360-marketplace-update