Many possible reasons. You're searching with too precise search terms. The family was missed. His name was mangled so that a wild card search fails. He was living in Scotland. He was in an institution somewhere and he's only shown by his initials. I'm sure there are numerous other suggestions as to why you can't find him.
Have you found him in 1891? Are you considering buying his marriage cert to get his father's name? Are you considering purchasing his 1874 birth cert to get both parents' names?