I’m not interested in telling you you’re wrong. You being wrong is your problem. I’m interested in my being right. If I can extract some information from our conversation that moves me to a better understanding of things then I have done all right from the interaction (assuming the time involved is short). The steel man allows me to extract this information from the interaction.
In practice, if someone isn’t capable of using the information I provide to re-assess their position, continued interaction is likely to be low quality. This isn’t a fault thing. It could just be that I’m incapable of interacting reasonably with this person. Either way, it’s then time to disengage.
Obviously it depends on the circumstance, but not every disagreement is about "winning" the debate. Sometimes the win is in building or saving the relationship.
Steelmanning is just applying the Least Convenient Possible World principle to debating. If you're picking nonessential nits then you might technically be right but you're probably also dodging the actual interesting questions.
The steel man locks the truth somewhere inside; and one doesn't look in case ones conversational partner feels offended by being wrong.
Of course you can't tell me I'm wrong; because you have to give my argument the best possible interpretation even if it doesn't deserve it ...!