Help Me Understand Why Error Coins?

Some people like error coins, some couldn't be bothered with them.
If the error is of a very minor nature there is no added value for such a coin.
The prospect of zero added value does not stop the serious student from persisting in the study of them.

Those who are only looking at possible rarity and added value of very minor errors usually give up. That is a pity. There is lot to learn in the study of error coins.
The numismatic student, on the other hand, ends up learning a lot about the minting process, and Mint technology. His interest may well then extend into other areas of numismatics.

I do, in fact collect major error coins, such as off metal strikes, patterns, brokages, piedforts, mules, severe off center mis strkes, coins struck without a collar, die adjustment strikes, severely bitten edges, and complete planchet failures, where the weight is affected significantly.

I have at least one example of each class of error mentioned, and in most cases, more than one of each.
It taken me more than 50 years to build such a collection. More than half of these have come from public auction.