Income taxes are dischargeable in bankruptcy if they are for a tax year more than three years ago and you’ve had the tax return filed for at least two years prior to the date of filing. There are some other rules I won’t bore you with. I’ll probably bore you with a lot of things, but not this right now.
A tax case requires that I get your tax transcripts to make sure all the requirements of tax dischargeability have been met prior to our target filing date. If those are met, then your income taxes are discharged.
The reason the government is letting you discharge your taxes is because you’re insolvent and trying to collect old taxes will just keep them from collecting future taxes, as you’re not made out of money, and the old taxes have doubled, trebled or more due to the interest and penalties tacked on. So paying them is unrealistic in the case of bankruptcy.
A more thorough treatment of tax dischargeability is here if you’re interested.