A family of Microsoft word processing software products for creating web, email, and print documents.
As you are aware, this involves not just changing the year, but changing the days and dates in each month.
Templates provided by Microsoft are often there because they look nice, not because they are easy to change or make good use of Word features.
They usually have been prepared by third-party developers/designers who are strong on aesthetics but not that proficient with Word.
(The same is true of report, letter and resume templates.)
Here are links to threads discussing this and solutions: How do I create a "Word Calendar Template" to show 2025 - see Suzanne Barnhill's Response
Do follow the links provided by Suzanne.
There are templates that can be changed and they are addressed in those linked threads.