There is no genuine organisational reason, it's just lazy computer program/form writing - they look at other forms from the same or other organisations, and just glibly copy what others do.
I've been through this with my own small business when we last did a GDPR review of our data. We could think of no reason at all why we needed to know whether a client was a Ms, Mrs, or Mr, so in accordance with the GDPR regulations, we deleted such data from our databases and removed the field from all our forms.
The only "effect" was that some clients (mostly more elderly ones) didn't like their letters being addressed to "Mandy Smith" and "Dear Mandy" and preferred it to be the old fashioned "Mrs Smith". That seems to be the only reason to justify keeping a "salutation" field in databases, i.e. for the benefit of the recipient rather than the organisation themselves, for communication purposes.
By the way, as part of the same GDPR review, we were a bit bolder and took the decision to delete any sex/gender fields from our databases too, for the same reason, that we didn't actually need to know if a client was a man, woman, or whatever, so again had no grounds to keep such data.