why is there no incremental backup in sql server [closed]?

It seems you are coming to SQL Server from an Oracle background and hence looking for similar terminology. Incremental backup in Oracle is similar to that of SQL server differential backup. Below is the definition of Incremental backup from Oracle:

Below is the definition of Incremental backup from Oracle: An incremental backup copies only those blocks in a data file that change between backups. A level 0 incremental backup, which copies all blocks in the data file, is used as a starting point for an incremental backup strategy. A level 1 incremental backup copies only images of blocks that have changed since the previous level 0 or level 1 incremental backup. Level 1 backups can be cumulative, in which case all blocks changed since the most recent level 0 backup are included, or differential, in which case only blocks changed since the most recent level 0 or level 1 incremental backup are included.

And below is the definition of Differential backup from Microsoft: A differential backup is based on the most recent, previous full data backup. A differential backup captures only the data that has changed since that full backup. The full backup upon which a differential backup is based is known as the base of the differential. Full backups, except for copy-only backups, can serve as the base for a series of differential backups, including database backups, partial backups, and file backups. The base backup for a file differential backup can be contained within a full backup, a file backup, or a partial backup.

Hope the above clears your concern.