So why didn’t they?

Because they didn't have a majority in the last two years.

Do you live in the US? The first half of the Biden administration was hamstrung by Manchin, Sinema, and the Republicans. The Democrats had nominal control of the presidency and legislature but faced implacable resistance from the Republicans and these two nominally Democratic senators. Until the recent Supreme Court decision the US hasn't had a king.

And Manchin had no real chance of reelection anyway.

With the existence of the Senate filibuster, passing laws is very difficult even when you win. There are entire topics where significant reform is basically impossible, from anyone.

This is why America's supreme court is so important: One can argue that most federal level changes in the last 8 years cane from the court just changing their mind on what used to be settled precedent.

The filibuster has existed for a long time and yet Congress was still able to pass laws. I don’t give them a free pass for this, they need to learn to work together with the other party like we did in the past.

I expect they will end the filibuster