AOC and her posse aren’t interested in beating Republicans in swing states; instead, they are interested in beating other Democrats. They want to shift their party further left, and replacing existing Democrats is the easiest way.
AOC found the magic formula. In Democrat-only districts (where only a Democrat can get elected), associates of her far-left posse only have to win the primary. This is far easier than winning an election; while the far left component of the Democratic party may be few, they are highly motivated. If they all come out for the primary they can easily outnumber all other voters in these historically low-turnout ballots. It’s how AOC gained her office; she effectively won the primary (and thus the election in her Democrat-only district) with just over 7% of her district’s Democrat votes.
Her strategy is obvious: win against other Democrats to push the party further left. It’s a good strategy, and likely to work if she is not stopped. The Democratic leadership had better run some moderate Democrats against her and her posse. Otherwise, I think the Democratic party as we know it is doomed.