once you start doing absolutely anything else (having a side job, renting out property, participating in the stock market, having income in multiple states, etc etc etc), you're in the byzantine territory of income/deductions/credits/AMT where nearly every line on every form involves reading the instructions for that line (and yes, nearly every line has its own instructions) and reflecting on your life to decide whether you think that purchase qualifies as a deduction, or what percent of your car's annual depreciation you can allocate as a business expense, or whether you need to declare your 2014 California refund as income on your 2015 Oregon taxes. Money ping-pongs around, getting taxed coming and going (you pay tax on your salary and tax again when you use that money to pay for gasoline (and a very few of these taxes are multiplicative instead of additive, so you can in fact pay tax _on the tax you're paying to buy gas_)).
I'm really not doing justice to the intricacies of the tax system. I would really enjoy reading a James Mickens tribute to it.
Pre-filled forms aren't going to help navigate the insanity, unless the governments (federal and all the states) have access to data about every transaction, every penny that flows through your household.