Why are wages (box1) social security wages (box3) and medicare wages (box4) all the same amount?

I assume you meant Wages (box 1), Social Security Wages (box 3), and Medicare Wages (box 5).

These are the amount of Wages that are subject to:

1. Federal income tax,
2. Social Security tax,
3. Medicare tax.

As Lisa995 notes, they are often the same because your wages are subject to all three taxes. However, sometimes one or more taxes don't apply to all of the components in your Wages.

A common example is contributions to a 401(k) plan. A contribution to a 401(k) is not subject to federal income tax (box 1) whereas it is subject to Social Security and Medicare taxes.

Therefore in the case that a taxpayer makes a $5,000 contribution to a 401(k) during the year, the amount for Wages in Box 1 is $5,000 less than the amounts for Wages in boxes 3 and 5.