This is because you're pivoting data which is essentially already pivoted!
In the attached is:
1. An ugly workaround added to your existing which is a calculated field. Don't use it, it's very inflexible (and it doesn't change if you add/remove things to the values area).
2. A second pivot at cell O3 which works as I think you want.
It's your data, unpivoted by
Power Query in the background and a new pivot table created from the result.
In the background your data is transformed to look like this:
2023-02-28_222447.png