The IRS's budget is $12.5 billion/year. Not sure what is spent on salaries. But probably a few billion a year given they have about 100,000 employees.

Having $50 million in unpaid taxes for an employee base like that is nothing. They probably have hundreds of employees undergoing bankruptcies at any given time for various reasons that weren't their fault like natural disasters, medical problems, fraud, theft, etc. There's also always going to be employees that "owe" taxes in cases where what they owe is in dispute, and will eventually get reduced or eliminated by courts.