SLC caching is only used on consumer SSDs, and on most drives it is largely or exclusively a write cache. Consumer QLC drives are pretty much the only ones that prefer to retain data in the SLC cache to accelerate read performance, rather than flushing it during idle times to prepare for the next burst of writes.
Or, presumably, using them in a miltitenant SAN or DBMS where the SSD’s pipeline is full of concurrent random IOPS to more than 15GB of hot data.