It's simple common sense. It really is.
Seth could be in Will's shoes any day of the week. He could leave WWE, go to New Japan and win a major title there like Ambrose did in his very first match. He's a top star and he's that good. He could be a BIGGER star than WIll in New Japan by the end of the month.
But Will can't necessarily be in the position that Seth is in. He can't necessarily be the champion of the top wrestling company in the world. He's only in the mid-card of the organization he's in at the moment... when he wins the IWGP title (which will probably never happen), THEN he can at least entertain the notion that MAYBE he could be what Seth Rollins is.