Because of years of circulation. Intentional damage, coin wrapper crimping machine.. There are a few ways.
Now You are asking unnecessary silly questions. Unintentional damage occurs in circulation due to different factors. The scratched up quarters could of been run over by cars for some time. Yes I have seen that happen many times. Intentionally damaging a coin is wrong but very bored crazy people do it and somehow it ends up in your pocket. They don't care about laws.
It's not against the law to deface a coin. Just think of elongated or rolled coins. What is against the law is making the coin into something different to change its value. The famous V nickel comes to mind. Just google Josh Tatum and you'll be surprised.
In the "kids art" world coins are damaged intentionally all of the time. It is also not against the law. Read the law. If you intend to deface a coin to make it something that it isn't and then intentionally use it above it's face value, then that is against the law.
I just use a drill, a toothpick and some glue and make little coin christmas trees for the kids. you can hole coins, and use the holes and many coins and make bracelets, etc. very common. Then you can press them and make them concave, or anything you want to do to them. Just look at "artsy" type websites for examples.
Yes as a matter of fact I have a 1954 D wheat that came off a bracelet still has ring on where they broke it off it looks like they chromed it to make it shine.
Exactly. For many *artsy* things it's not "why would someone do that to a coin" , but rather "why not, to get the end result that they want" (which may take many iterations of failed attempts).
When I was researching that penny I also found out that back in the 50's in automotive shops in schools they would dip them to learn how to plate metal.
Yes I have even seen some of them with burn marks on them. Hey how about the power of the penny making batteries.