They didn't do everything they could to stop Trump, Democrats showed there was one step further they could take: have everyone drop out and endorse a single candidate. Republicans also didn't rig any of their primaries, and I'm pretty fucking sure Democrats did n Iowa (and as someone from Iowa I'm still mad about how they basically just sacrificed our state)
You talk a lot of shit. Did you even volunteer for Harris? Do any canvasing? Door knocking? Phonebanking? How much did you donate? My guess: you did literally nothing.
Maybe that's true!
Out of all the people that voted for Harris, how many of them do you think actually volunteered any time at all to her campaign? I'd guess it wasn't even 0.1%.
What you're accusing the US left of, of being armchair whiners, applies to nearly all USAmericans. People in this country believe politics is just complaining and voting every couple years, and this is true of Democrats and Republicans and Independents. The actual political engagement in the US is extremely low and it's a serious problem.
I'll choose to believe you, but you should realize you're a rarity in the US. Half of us don't even vote!