I don't think I had bloodworks done on my cats either when they were neutered,but they were kittens and otherwise healthy.
Now,when my cats are older,whenever they need anasthesia,I usually have bloodwork done before,the same as would be done with me,should I need surgery.
With stray animals,it probably is needed,although shelters and rescuers are trying to keep the costs down,since there probably is not enough money available,nobody knows their over-all health,which GG sadly discovered:sad:
It seems to me though,bloodwork is pushed by the vet,I was told since Rocky is 10yrs(I thought he was 12
) old and Chico 9yrs,they need bloodtests every year.