Why do they focus on one Republican in NC when the ballot harvesting fiasco was wildly and obviously present all over California?
Because the California legislature and the Governor passed a law making it legal to do in California what is still illegal to do in North Carolina. It's legal in California (in spite of the law saying the election must be held on the first Tuesday in November) to vote absentee after the election and for third parties to take those absentee ballots to the vote-counting centers. In other words, if you have a close race in California and the Republican in winning, in the next few days after the election you send people around to those who haven't voted (as in California it's open information if you voted or not) and who have registered as Democrat or are in a heavily Democrat demographic, have them fill out a ballot (or fill it out for them), bundle it with similar ones - enough to change the outcome - and presto-chango, the Republican loses and the Democrat wins.
By concentrating on the NC incident (and ensuring that it gets lots of news coverage), the average know-nothing voter will learn to associate “voter fraud” with “Republicans”. It neutralizes the issue for Dems. And if we try to raise awareness of voter fraud in 2020, it’ll actually cause negative blowback for Republicans.
It’s a tried & true Dem tactic. Works like a charm every time.