Because you had immunity to shingles (from having had it) and therefore not needing shingrix?
Shingles is a bit of a special case.
As you probably know, it is due to the reactivation of long dormant chickenpox virus "sleeping" in a bunch of spinal cord neurons (hence the rash pattern often fitting a dermatome (=skin area served by a nerve).
So by definition, you have already been exposed to, and have immunity to, the culprit.
What happens in Shingles is that at some point in later life (or when seriously immunosuppressed), the immunity falls below a threshold, and the virus reactivates. That usually gives you renewed immunity for a variable period, which may be the rest of your life - or not, depending on your immune system.
The point of Shingrix is to boost that immunity without paying the price of a Shingles episode.
Now, you usually do not want to give a vaccine soon after a manifest infection, for Shingles/Chickepox or anything else like Covid etc, because the existing immunity dampens the immunization, so you recommend waiting for a period of time, usually until the humoral (=antibody) immunity wanes, ~ 3-6 months.
Those considerations need adjustment in special circumstances, such as evidence or suspicion of weakened immunity, such as disease, chemotherapy, recurrent bouts of the infection (!) etc, where it may be preferable to vaccinate anyway.