Because it's trendy. Some never saw him play, others just watched or remember his second season at United. Even then, he wasn't as bad as Onana.
He was the youngest GK to ever win the Champions League at the time (Marseille, 1993). He also played a major part when France won the WC and the Euros back to back (1998 and 2000).
Very composed under pressure, he had a great left foot as well, and was known for his quality distribution. His only (relative) weakness was crosses, in great part due to his lack of height.
Seeing him being compared to Onana is absolutely hilarious and tells you quite a bit about the poster and their football knowledge.