Future obligations for which you have not yet received the benefit, such as guaranteed contracts and lease obligations, are not debt from an accounting and business valuation standpoint. They are things that any going concern is going to have. These items are baked into the value of the business. Things like future contracts are never considered debt in this context because in paying those obligations, you are also receiving the benefit of player performance or use of the stadium or whatever, and these benefits generate revenue.
Debt in this context is future obligations for which you have already received the benefit - aka loans. Not every business carries debt on their books - it is a choice to fund your operations (or withdraw the proceeds to use to fund other operations) with debt as opposed to equity. That is why the assumption debt (not all liabilities, just debt) has to be considered when selling a business. With loan debt, there's no revenue-generating benefit in the future. It is a straight-up cash outflow.
Think of it this way: you have two identical companies - same lease, same future contracts, same revenue - only one is free and clear of debt, but the other is carrying significant debt like the Twins. Their values of their operations are identical, but no way anyone pays the same for the two teams. Either the prior owners assume the debt, or the purchase price is decreased to account for the additional obligation.