If citizens have sufficient amounts of yearly income deducted via normal payperiods, why file yearly taxes?

other than receiving funds returned, is the April deadline that important?

Well, considering you are paying the federal and state governments via withholdings on a weekly, bi-weekly, semi-monthly, monthly, etc. basis, they have your money, and if you've overpaid them, you'd like it back ASAP, and if you've underpaid them, they generously give you till April 15th to pay what you owe them. Plus, a lot of people have income other than wages, they have interest, dividends, capital gains, rental income, business income, unemployment, social security, pensions, IRA's, etc. that fluctuate from year to year, so it's awful hard to come up with exactly how much you'll owe the IRS and the state from that income.

LIKE A BANK. THE GOVERNMENT PLAYS WITH OUR MONEY... INTEREST FREE. THIS IS HOW THEY SURVIVE. ITS B.S. BUT UNTIL WE STAND UP FOR WHAT IS WRONG WE LIVE WITH IT

Just as corporations file annual reports, so do taxpayers.
If income tax were due in April, it would be a hardship to many people, so we deduct taxes , "as you go." The amount is merely an estimate..and the filing of the return is an accounting. If we with hold too much, you get a refund. if not enough is withheld, you owe a balance due.

It would be almost impossible to fine tune
it to the point where your tax equals the tax withheld, and no one owes anybody anything.

Anybody out there either owed or got back less that $ 20.00??????

Very simple reason, reallly. The self-assessment is voluntary. It's up to us to know the rules and claim whatever tax benefits we're entitled to. If we fail to do so, and the government estimates that we don't actually owe anything, they are quite OK with failing to file or filing late.

Most countries assess income tax at the source. For example, in the UK it's up to you to coordinate the mortgage tax relief with the lender and your withholdings with your employer rather exactly. (You can self-assess, but the government doesn't encourage you do to so for obvious reasons.)

If you only have W-2 income & feel that you have had enough withheld during the year, you can certainly choose not to file a return. If you're due a refund, the government will be happy to keep it. If you have expenses that would allow you to itemize, such as real estate taxes, medical expenses, mortgage interest or if you make substantial contributions to qualified charities, the IRS has no way of knowing this information. They'll calculate your return with the information that is available to them. If you have interest or dividend income or any other type of income that would be reported on Form 1099, possibly subject to self-employment tax, with expenses that might offset the income, the IRS would only have the actual 1099. Again, they would have no information on expenses to offset the income. And the April deadline is when you can file & pay any balance due with minimal penalties & no interest.