Cops don't do anything about theft if it does not rise to level of a felony period. Most shoplifters don't get arrested until they hit felony level either.

Reason they get arrested for felony shoplifting is big box stores gift wrap those convictions. They have watched them, tracked exact items they have stolen down to UPC with price, have all the video/spreadsheet and it's all handed to cop/prosecutor on DVD. Those cases are so easy for prosecutor because conviction rate is ~100% and any testifying required is all paid for by big box store.

On bigger note, as society, we don't know how to handle people who have antisocial behavior. I'm not talking big stuff but low-level stuff that still impacts quality of life.