Many devices out there utilize 3 pin DMX ports. This does not mean they are bad; DMX only requires 3 pins to pass data, and a 3 pin connector can save on cost.
If you have a primarily 3 pin inventory, it makes more sense to have 3 pin DMX on hand instead of adapting 5 pin cables all the time.
CAUTION: A 3 pin DMX cable is not the same as an XLR microphone cable. They use the same connectors but the cable is different. They have a different impedance. While using one for the other will technically work, it can cause data issues. Better to be safe then sorry.