Medellin has a LOT of taxis. On several occasions I have heard the taxi fleet referred to as the “mancha amarilla” or yellow stain. If you look at traffic downtown many times the predominant color is yellow.
In some ways this is good. It is almost always possible to catch a cab anywhere in the city within a couple of minutes. It does contribute to the traffic congestion significantly. A lot of people here can’t afford their own car so the combination of the Metro, buses and taxis is an inexpensive alternative.