Maybe just because he was a young kid at the time and (I'm guessing probably around 15 - 20 years pass between the end of Wolverine and the start of X-Men) he had just forgotten him.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist