The impact factor is an important metric for WoS journals, but not all of them have it. This depends on several factors:
First, WoS has four main collections: SCIE, AHCI, SSCI and ESCI. Only the journals in SCIE and SSCI have an impact factor. The journals in AHCI and ESCI do not have an impact factor.
Second, a journal needs to be in the core of WoS for at least two years to get an impact factor. This is because the impact factor of the current year is based on the data of the previous two years.
Third, a journal can lose its impact factor if it is removed from the core of WoS for one or more years. Even if it is reinstated to SCIE or SSCI, it still needs to wait for two years to get an impact factor again.