In response to the United States' killing of an important Iranian military commander on Iraqi soil on 3 January 2020, the Iraqi parliament voted to expel US troops from the country. According to various news sources (such as Al Jazeera), this decision is non-binding as it took the form of a parliamentary resolution rather than a legislative act.
Why did the Iraqi parliament choose to respond using what looks like a consultative or advisory proclamation rather than a binding decision with the force of law? Is this because they wanted to issue a forceful-sounding message of displeasure without actually wishing the US military to leave? Or is it because the procedure for passing binding legislation rather than a parliamentary resolution is much more difficult and perhaps less likely to be successful? (For example, are there more stringent quorum or majority-voting requirements for legislation?) If the latter, are Iraqi legislators now preparing or debating legislation that will formally effect the expulsion?