saley,

Причина в том что
https://docs.microsoft.com/en-us/sql/t-sql/functions/last-value-transact-sql?view=sql-server-ver15rows_range_clause further limits the rows within the partition by specifying start and end points. For more information, see OVER Clause (Transact-SQL).
Переходим по ссылке
https://docs.microsoft.com/en-us/sql/t-sql/queries/select-over-clause-transact-sql?view=sql-server-ver15ROWS/RANGE that limits the rows within the partition by specifying start and end points within the partition. It requires ORDER BY argument and the default value is from the start of partition to the current element if the ORDER BY argument is specified.