SQL Server database is too large because available space allocated 70% mdf space
The &quot;unused space&quot; is reserved by extents of pages which are maintained to be allocated to your data as your Tables and Indexes grow. The reason it's as big as it is currently is because you had a growth event at some point in the database that caused the MDF to grow.
General recommendation is to not shrink the file back down because it's likely that unallocated (and even unused) space will become allocated and used, and growth operations are heavy and affect performance. (There's also potential risk of data corruption as a result, when doing it to the MDF.)
It is not uncommon to have about 50% of your drive space in Unallocated. You can read more about Unallocated Space here. When SSMS calls it Space Available, it's already reserved by SQL Server but available to become allocated as needed.