It's been like this a while now since mid 2020 with all Amazon webstites since covid-19 started to affect countries around the world.
Amazon USA for example for months you can't do a pre order if delivery address is in UK or EU
Amazon Canada stopped doing pre orders also for customers based in UK/ EU a good few months also.
Amazon EU lot of pre orders can't be done unless you are based in that Amazon country
Example Amazon Germany will only take pre order if your delivery address is based in Germany.
If you are based outside amazon country website that you want to do a order with
After release date when item is instock that is when most times you can do a order but some items after release date you may see not available.
It's the same for Amazon UK you will need to wait until after release date to do an order if you are based outside UK
It's to do with lack of international flights due to covid-19.
A lot parcels are on flights that passengers use
Amazon also give priority to essential goods over non essential
A DVD/ Blu-ray/UHD disc is not essential goods
Only a few couriers example UPS have their own fleet of aircraft.
Most air mail goes on passenger flights but due to covid-19 there is lot less flights available and not often known in advance when a flight will be available.
Amazon Canada will take pre orders if you delivery address is based in Canada for example.
Some post has been using sea transport instead.
UK leaving customs union also now effects Amazon UK and other Amazon EU websites and thats on top of covid-19 affecting delivery
Amazon won't know for sure which Amazon warehouse be it in UK or EU will have the stock mostly until just before or after release date
That is why you will also have to wait until after release date.
You might see some pre order items as availavle to order a week before release date if you are based outside UK
I'm based in Rep of Ireland
Rep of Ireland members using Amazon UK
Most my orders from Amazon UK since January 1st 2021 will now be shipped from a Amazon warehouse based in France or Germany instead of a UK warehouse with very few from a Amazon UK warehouse
Some stock of UK/Ireland releases from distributors now needs to be sent to Amazon EU warehouse instead of a UK warehouse
When Amazon UK dispatch from UK or EU warehouse it now goes to Amazon Ireland logistic distribution center based in Rathcoole
Amazon Ireland logistic distribution center based in Rathcoole was setup in October 2020
Items are then delivered by An Post or by a Amazon Ireland logistic van driver
Since January 1st 2021 Tracking will list courier now as Amazon Logistics
You parcel will be delivered by An post or a Amazon logistic Van driver or by DPD
You get a email when out for delivery or if you use amazon app a message when out for delivery