Why do California and New York need so much time to count their votes compared to other states?

Question

As per the New York Times, California has only counted 89% of the votes so far and New York has counted 84%, even though its now been nearly a full week since the election has been concluded. Almost every other state is showing up on the same map as having more than 98% of the votes counted, so presumably they're pretty much done tallying up the votes.

Why do these two states need so much time? Mail voting cannot be the only reason, as states like Oregon or Washington are pretty much done counting despite having all-mail voting in place. Surely the vast majority of ballots would've been delivered via the postal system by Friday at the latest?

Answer 1

California

The California Secretary of State has a page on their counting process. The most relevant portions from that page seem to be the following (emphasis mine):

Why have some counties not reported any results immediately after the polls close?

Each of the 58 county elections offices processes ballots differently, and the distances poll workers must travel from polling places to county offices vary greatly. State law requires county elections officials to send their first batch of results to the Secretary of State’s office no more than two hours after they begin tallying votes after polls close on Election Day. County elections officials continue to report results periodically on Election Night until all precinct vote totals have been reported. County elections officials will continue to count ballots up to 30 days after Election Day.

When are vote-by-mail ballots counted?

Vote-by-mail ballots that are received by county elections officials before Election Day are typically counted on Election Day. Many more vote-by-mail ballots are dropped off at polling places, drop box locations, or arrive at county elections offices on Election Day. Due to urgency legislation For this election vote-by-mail ballots postmarked on or before Election Day and received by county elections officials no later than 17 days after Election Day must be processed.

Depending on the volume of these types of ballots, it takes up to 30 days for county elections officials to verify voter records and determine if ballots have been cast by eligible voters. The frequency of updated results will vary based on the size of each county and the process each local elections office uses to tally and report votes.

How will we know how many ballots remain to be counted?

Two days after the election, counties must provide the Secretary of State an estimate of their remaining unprocessed ballots report. The Secretary of State’s office will post this “unprocessed ballots report” online and provide daily updates as new estimates are provided from the county elections offices.

The report mentioned in the last quote is provided here. The page was (last) updated on November 10, and the estimated total remaining unprocessed ballots state-wide is 2,097,466 votes. It should be noted that estimates for some counties are outdated. Based on that report, we can also see that most unprocessed ballots (1,692,175 state-wide) are mail-in votes.

New York

I've not been able to find a summary for the situation in the state of New York as a whole. I have found some more local reports which reflect a story similar to the one above.

Absentee ballots in Onondaga County

From waer.org:

Absentee ballots are still arriving at the Onondaga County Board of Elections, and commissioners are preparing to spend more than a week counting them. Democratic Commissioner Dustin Czarny reminds us that it’s normal to count ballots after the election because military voters have regularly sent in their ballots from overseas.

The county has received around 56,000 absentee ballots, and the counting will begin on Monday. Czarny says it could take a while.

“We will probably need all of next week- maybe the week after. It really depends on how slow the process goes because we have observers from the different campaigns that are close, and they can slow down our count pretty quickly.”

In this quote, Monday refers to the Monday after the election (November 9th). The last paragraph refers to the two weeks starting that Monday the 9th. Given that today is only November 10th, the timetable fits that these ballots have not been tallied and reported yet.

Mail-in ballots arriving after election day

In New York State, it seems mail-in ballots may be counted if they arrive within 7 days after the election. So votes that arrived by today (November 10th), may still be counted. According to timeout.com:

Governor Andrew Cuomo signed a new package of election reforms into law this week that allows New Yorkers to get an absentee ballot if there's a risk or fear of contracting COVID-19 (or any illness.) It'll also make it so the Board of Elections must count all ballots postmarked on or before Election Day and received within seven days after Election Day (that's November 10). Those ballots received on November 4 (the day after Election Day) without a postmark must also be counted.