There are millions reasons that owner owns the TAX. However, buying the TAX lien property is to gain the higher interest that is guaranteed by local government, 99.9% case that you will not own the property at all. So if you have 5W, you would bid 10 or 20 5W tax lien properties to maximize the gain.
There are alots book on this topic, actually, the guys who wrote books made more money than the TAX lien property buyers.