California couple

I am working on a RDP return. They will file jointly on their state return as allowed for an RDP. For the Federal return a RDP is not recognized so they will file single. My question is, IRS states that RDP's adhere to their states community property laws. Meaning both partners need to report one half of each other's incomes on each Federal return. 

I have had a few people file Married Filing Separately (California residents). I have never shared income on their federal returns. They have never been audited or faced any issues from IRS. Why does an RDP have to report shared community property (W2, 1099G, etc..) income but MFS do not?