By default, each histogram has 20 steps which provides good performance and modeling for columns that have an even distribution of values. A higher number of steps can increase the accuracy of I/O estimates for:
Columns with a large number of highly duplicated values
Columns with unequal or skewed distribution of values
Columns that are queried using leading wild cards in like queries
If your database was updated from a pre-11.9 version of the server, the number of steps defaults to the number of steps that were used on the distribution page.