You might go years without doing one on the line (you will always practice them at the six month simulator checks,) or you might do two in the same week.
It is a standard flight profile if there is any reason for not completing the landing.
Those reasons are many and varied:
The runway may be blocked by another aircraft. That may be because it is late commencing the take off roll. It may have abandoned its takeoff. It may be late vacating the runway after its own landing. It may have a radio failure or other technical fault. It may also be that the runway is obstructed or threatened by a ground vehicle.
For the above and other tactical reasons ATC may instruct the approaching aircraft to "Go around."
An aircraft must be stabilised on the approach usually by 1000ft, but certainly by 500ft at the latest. If it isn't then it should ordinarily "Go around."
The aircraft can be unstabilized by a myriad of factors that include such things as poor weather, late tactical changes, rushed approaches. If an aircraft isn't stabilised within laid down parameters, then standard operating procedures and good airmanship, will usually require a missed approach (go around) to be carried out.
The crew can also carry out a missed approach at any time (and not withstanding the above,) they deem it necessary or prudent.
Missed approaches are not uncommon in themselves, such that at any major airport they will almost be a daily occurence to some degree, however for the individual pilot or indeed passenger they are not a particularly frequent occurence, although as I say you may get lucky/unlucky and have two the same week.
I should also point that out, that "fly by wire" has little relevance to the incidence rate, for the reasons already given. Likewise, automatic approaches, (which are rarely conducted outside of conditions requiring their use,) also have little bearing on the frequency of the event.