Most of us don't have the software to interpret them
Speak for yourself.
Well, very few people use pgp signatures on the list.....
Some may HAVE the software, but have the good taste not to use it when there is no point.
For the record, roughly 21% of mail to this list is signed. I am not sure if that fits your definition of 'very few'...
pgp00000.pgp
Description: PGP signature