I see two major reasons for that. One is that Wilmslow is in the so-called "Golden Triangle". Manchester United footballers, actors from Coronation Street, and business people with quite a lot of money live there, and those people need to travel to Manchester and London on a regular basis. Congleton, on the other hand, is a former mill town with a fairly low profile. When my late mother lived in Congleton as a girl, "going to the match" meant Port Vale rather than Manchester United, and you went on the bus (which you pronounced "buzz").
The other is that Congleton station is awkwardly located a mile east of the town centre. If you live the other side of town, you can probably be in Macclesfield via bus quicker than you can walk to the station.