Because when you realise it was only the paint blister holding it together, it commits you to fixing it when it crumbles away.
It went something like this....
"Gosh, Mrs LTs Golf looks very nice when it's had a good valet, but I really must get round to addressing the blister on the front wheel arch - I'll give it a little prod to see how solid it is under the.......... oh."
So now I have about a 4" length where the return flange has crumbled away and three 1mm perforation holes in the flat face of the wheel arch edge.
What to do.
1) Cut away any remaining rust and botch it with P38 and do an obvious local touch up with a small spray gun. (You can imagine how much I'd loathe to do this and how much this goes against the grain).
2) Buy a used wing from eBay for about £30 that will almost certainly have it's own rust issues and almost certainly not be in the correct colour and hence would need spraying properly but will fit and allow a quick swap over.
3) Buy a pattern wing from eBay such as this which is cheap enough... https://www.ebay.co.uk/itm/VW-GOLF-4...AAAOSw7QBcoiko
and have this painted properly to match - but will it fit being a pattern part? Are late model pattern wings a decent enough fit?
4) Remove the original, weld it up properly and have it painted to match, but taking the car off the road too long which I can't afford to do as it is required daily.
The car is worth £750 so I can't justify big expense, yet it is a great car, wants for nothing (bar a front wing) and has plenty left to give as cheap motoring, plus Mrs LT loves it and is very attached to it. It won't ever get another timing belt, but there's 3 years left in the current one so this isn's a pre-sale tidy up.
I put it to the people.... what should I do?
The key thing is that the car can only be out of service for a day, absolute tops, which is about how long it would take me to remove and replace a pair of front wings that were ready to go.