Congress *did* act. They impeached him twice. The second impeachment was specifically about incitement on January 6th, and 7 Republicans voted to convict. That's not nothing. What you're really asking is why a supermajority didn't vote to convict - and the answer is that 43 Republicans refused to hold him accountable, claiming either that it wasn't impeachable or that it was a political witch hunt despite Trump's own lawyers not seriously contesting the facts of what happened.
The Raffensperger call? Recorded. The fake electors? Documented. January 6th? Broadcast live. The Manhattan DA convicted him based on trial evidence. Sworn testimony from his own appointees - Barr, his Attorney General, his DHS officials - confirmed there was no fraud.
So did Congress fail? In one sense yes - they failed to enforce accountability uniformly across party lines. But saying Congress wasn't there is rewriting history. They investigated. They impeached. Some voted to convict. Some didn't. That's Congress working exactly as designed - badly, slowly, and requiring moral courage that half the chamber didn't have.