What kind of awful subway is it, that takes 35 minutes to drive 7 stops?

I just checked a Rotterdam subway line and it does 30 stops in an hour[0] which is a ~32KM distance as a bird flies[1].

[0] https://www.ret.nl/home/reizen/dienstregeling/metro-b.html [1] https://www.google.com/maps/dir/Nesselande,+Rotterdam/Hoek+v...