The change was down to customer demand (to use a well-worn phrase). The shop found it uneconomic to stock both frequencies and the 433 MHz option was by far the most popular.
If you ask nicely, I think it might be possible to buy units without the r.f. module, so that you can fit the 868 MHz module yourself.
I don’t advise trying to unsolder the r.f. module, unless you have access to the proper professional workstation and the skills to go with it.
