Why not? The Democrats would have won 5 of the 6 elections this century if it were popular vote instead of the Electoral College. (And that last one would be suspect, too, it was George W Bush’s reelection. If he wasn’t elected in 2000, who knows how the 2004 election would have played out.)
Because it's not happening. Constitutional amendments are just very much off the table in the immediate future. The interstate popular vote compact is an interesting idea but it's going to stall out far short of deciding the election. And it's not a high salience issue for many voters.
Harris is militaristic (pledging unlimited support for genocide, making the US the "most lethal in the world"), far to the right of where Biden ran on immigration in 2020 (they basically adopted all of Trump's policies against refugees and the bipartisan border bill was pure fascist shit), they dropped opposition to the death penalty from the platform, she's pledged to put a Republican in her cabinet, they want to roll out more trade war bullshit against China, she has completely backtracked on fracking and now wants to expand it, and it looks like she's going to replace the FTC chair with a probusiness puppet to protect US monopolies.
She's basically al 2000s Republican. Hence, Dick Cheney endorsing her.