The plans cache of my SQL Server is only containing stored procedure objects

Question

I have noticed that the plan cache of a SQL Server I manage has only stored procedure objects. There is neither prepared nor ad-hoc ones, even although I have executed some dynamic parameterized queries for testing whose plans should be cached as prepared.

The machine has enough memory so it is not due to a lack of resources.

Any idea about to what this could be due?

Thanks in advance.