It's not just a technical issue, but also the tax law itself has changed. For example, you used to be able to fill out a 1090-EZ for your taxes if all you had was W-2 income and bank interest. Anyone who meets that criteria could complete it in an hour. But that "EZ" form has been completely removed and replaced with a vastly more complicated one. If your tax situation is just ever so slightly unusual, things get real complicated, real fast.