Because that is what the legislature included i the Statute
Please note that THESE COMMENTS ARE NOT INTENDED AS LEGAL ADVICE and are for informational purposes only. This response is not intended to create any attorney-client relationship and is only based on the limited facts given. The response might change should additional facts be learned and should not be relied on as legal advice. It is recommended that you consult with an attorney who can properly assess the situation, as well as all pertinent facts, prior to taking any action based on the foregoing statements
DSHS requires two years (the most recently years) of tax returns information for modifications of child support so that they, and the Court, can better understand the parties' current and historical earnings. This applies to all child support modification cases, whether they include DSHS, or not. The Court's need the information and the statute requires it.