As a retired air traffic controller with over 35 years experience I would say the most common cause is a blocked runway. The go-arounds I experienced due to a/c technical problems were few and far between. Blocked runways can be caused by many factors - landing a/c ahead bursts a tyre (fairly common)... one ahead misses a turn-off and has to go to next one... towing a/c slow to clear, etc. Also a runway inspection may turn up a broken light fitting or something similar. Some way down the list would be go-arounds due to LVPs - maybe many on a single morning but over a long period they would be comparatively few.