This is the STRATEGY used by SQL server to avoid locking a large number of database resources. The locking on resource use lot of memory spaces. Let's try to understand this by a use case where we have to apply locks on 30,000 records where each record size is 500 bytes for triggering DELETE operation. If we CONSIDER the memory space requirement for the above use case then we would be requiring one shared lock on database, one intent lock on a table, exclusive locks on the pages would be in the range of 1875 and around 30000 exclusive locks on rows. If we consider 96 bytes size for each lock then total memory space requirement would be 3MB for single delete operation.

To avoid such a  SQL server leverage lock ESCALATION strategy. This will prevent the need of large memory space requirement by escalating those locks to single lock instead of many locks. So in cases where we need thousands of locks on many resources, lock escalation will ensure single lock which will fulfill our OBJECTIVE and at the same time taking care of memory space issue. The exclusive lock on the table will ensure that we do not need page level lock to ensure data integrity. Instead of having so many locks required on many COLUMNS and pages lock, SQL Server will escalate to the exclusive lock on a table.