What this article misses is that the line 10 expansion to the north was a clear attempt at gaining votes and not an attempt at designing a good subway.

If you look at the physical map, you will see that it visits multiple towns that are not in a straight line from Madrid. This causes the line to "zig-zag" and what should take 20 minutes in a straight line becomes a 1h 15min ride.

People use it because Madrid has started being hostile to cars and the only two alternatives are trains (which is pretty good, takes 30 min) or buses

It's also not 24/7, closes at midnight (and if you are going out in Spain, you will stay way later than that)