Using accelerometers is the traditional way to measure mechanical vibrations, as mentioned in the ISO 10816-3 specification as example and they will provide then acceleration and velocity values. It is true that microphones have much wider bandwidth, but then they also pick up easier un-wanted signals from the full measurement band. They also give out the value in SPL, Sound Pressure Level. For mechanical vibrations, accelerometers are then better to use when microphones can provide specific information in hearable audio or ultrasound frequencies, microphones can then be used for many different other applications also (gas leakage etc).
