Because that’s the standard and that is the wage I negotiated and my bi-weekly checks are that number/26. I didn’t negotiate a per-payperiod rate.
It’s what my taxation is based on.
It’s what all my credit applications ask for.
Also, what you make and what you take home are really quite variable based on circumstance between 2 people making the same base wage. Retirement contributions, health care premiums, taxes, and other deductions vary from person to person.
For salaried employees it’s the standard metric by which wages are measured. You don’t need to guess anything. That’s the standard.
For hourly employees, that would be your hourly rate. Since hours can be variable and overtime is a thing your yearly rate would be variable too.