It's not about the series itself, it's about on how they saw he was so popular, they made a whole series with him being the MC.
You're ignoring Wolverine wasn't created as an X-men member, he was created to be a Hulk's villain, then he got incorporated to X-men. Do you know Wolverine was one of the most mysterious characters in Marvel during 90s and that what made fans gettig interested on him? Lol
Imo, Wolverine made part of X-Men, Avengers, F4 and Midnight Suns.
Hold up pal, Deadpool's popularity doesn't top Wolverine's, the only Deadpool movie which broken 1b box office was exacly "Deadpool and Wolverine" lmao, and Deadpool's game ain't even popular, it floped so hard lol