Call it an educated guess if you want, but after years of doing corporate work as a lawyer for small businesses and larger corporations, I have a strong suspicion of why Trump will not release his tax returns.
It should be abundantly obvious at this point that Trump is not worth nearly the amount of money he claims to be worth. I suspect Mark Cuban is right that Trump is worth well less than one billion dollars. To be sure, however, an income tax return will not show net worth. What it will show, however, are business expenses and annual income.
There are a lot of very wealthy people who have high net worths who appear not to have a lot of income. But Trump is in a peculiar position. Trump is a brand. That brand is wrapped up in the Trump Organization, which is supposed to be a corporate entity.
If Trump released his tax returns, I suspect it will show that Trump has been commingling his personal income and corporate assets. For example, when Trump makes personal trips on his airplane to Mara Lago, is that a corporate expense or a personal one? And if the corporation covers the costs to the holding company for the plane, do they treat it as a deductible expense or is it attributed to Trump as a taxable fringe benefit.
Likewise, assuming Trump’s annual income shows he really could not have the cash flow to be making multi-million dollar loans to his political campaign, that’d raise further issues about commingling of corporate and personal assets. Once that is shown, a creditor or plaintiff could “pierce the corporate veil,” i.e. go after Trump personally for claims against his corporation.
In other words, were Trump to release his tax returns I suspect we would see two things. First, he has been lying about how much money he has and second, he would show he treats his corporation as a personal extension of his brand, which is a big no-no for tax purposes.