The SAP Enterprise customers have strict availability requirements and to meet these KPIs, architects look up to clustering solutions to meet the requirements. The Windows Server Failover Cluster (WSFC) is one such cluster solution. It's available as part of Windows Server Datacenter edition deployments. This makes it a default choice for setups that are using Windows Servers.
Note that the SAP HANA database is only currently released for Linux (SUSE and RHEL). Hence in such setups, the WSFC can be used for SAP Central Services (ASCS/SCS). For MS-SQL deployments, the WSFC is also used to provide high availability with SQL Always On.