As Curious wrote, it can depend on many things, Alffe.
My daughter has them because she has structural problems in her ureter (not her urethra). She's only got one kidney and ureter now, but that ureter remaining is called a Megaureter and it pools urine because of the shape so never actually voids all the urine that should be going under pressure from the kidney to the ureter to the bladder. Some people also have problems with the ureter at the entrance to the bladder. Like a valve that doesn't quite shut tightly enough, it will allow some urine to push back up into the ureter.

In her case the problem is in the ureter and kidney rather than the urethra so she's more prone to actual kidney infections. The urethra is the part that goes from the bladder to the outside. That's where most people get the problem. Drinking more water and being really hygienic can help. Cranberry juice is good. Can buy it in capsules as well. Doctors recommend no bubble baths too. Showering rather than actual bathing is better if someone has a UTI although that type of thing doesn't affect my daughter because her problem is more internal.

Some people do seem to be more prone to them than others. If they persist people need to see a doctor. That's really important.