I've experienced quite a few go arounds, almost all of them are explained as "aircraft in front didn't vacate the runway in time". I'm a little bit suspicious that this phrase is used by the pilots so as to not spook the passengers. Is this phrase the norm or do you usually announce what the issue was?
Airlines have entire departments devoted to marketing, aka, spin, and the pilots don't belong to them.
For us, it is much simpler to give a very short version of what is actually happening. I don't have the time for elaborate tales, when most of my attention is on the go around, sorting out whatever issues there may be, and then flying the next approach.
The aircraft in front being too slow (on the approach, to clear the runway, to cross the runway, to take off, and so on) is a very common problem, which, if anything, is getting worse as the traffic density at airports increases. Very large aircraft don't necessarily help either, as they can be very slow to get moving. Sometimes that's the pilots' fault, and at other times ATC seem to suffer a fit of wishful thinking.
I can recall a 767 departing in front of me from Melbourne 16 (as I approached in a 767). ATC had left plenty of space, and he was quickly off the mark. All looked good until he had to abort. So, there are lots and lots of reasons.
Go arounds are caused by:
Weather (especially wind)
ATC / other aircraft
Mechanical issues / warnings
Pilot mistakes (generally too much energy)