My grandson drives a Mercedes 2001 van; the front passenger wheel fell off while driving, but the wheel nuts remained in place, and did not come off. The holes on the wheel had been enlarged enough for the wheel to fall off. What could cause this to happen?
It seems to be an extreme case, but if the lug nuts were not fully secured against the rim, the forces involved in driving can erode the holes in the wheel, especially if the wheel is not steel and is a softer alloy of metals.
In a static position, the wheel stud is resting in the portion of the hole in the wheel farthest from the center. If the nut is not tight, there will be space above the wheel stud. If the nut is partially tightened, it will keep the wheel against the hub but will not keep the wheel from moving around the stud.
As the vehicle travels, each succeeding wheel stud moves as far away from the center of the wheel as possible, simultaneously as a diametrically opposite wheel stud is moved closer to the center of the wheel. This rotation causes the space also to "relocate." The space does not really move, it's the wheel that moves, wearing against the wheel nut, wearing the smallest amount.
At normal travel speeds, this is thousands of times per trip. Eventually the wear becomes so great that the movement is increased, along with the acceleration of wear. A "sensitive" driver would have noticed changes in handling, especially while cornering. It should have been detected earlier as you've noted it was a front wheel and should have been felt as a vague feeling in the steering wheel.
Overlooked in my answer is the possibility that there is a mismatch between the lug nut facing and the wheel facing types.
Amazingly to me, it does seem to be a thing that, if you drive with the lugnuts not correctly tight, the holes can be deformed / enlarged / oval-ized a bit.
The usual mechanic's word for this seems to be "wallowed" (various spellings).
If you type exactly this in to google:
"car wheel bolt holes wallowed"
you may find some information.
To me it seems incredible that the holes would wallow-out so much that they would, all five, be uniformly bigger diameter than the actual nuts, and all of this without destroying the studs or the vehicle being totally inoperable anyway.
I'd say any copper would suspect some sort of crime or bizarre prank or such.
(Random example. A tire store totally forgot to put on the lugnuts, the wheel fell off, and then when the tire store guys ran over to see what happened, someone quickly screwed the nuts on to the now-demolished car whilst yelling "wow the wheel popped over the lugnuts!" or such.)
Anyway "wallowed" seems to be yoru search term for more information.