For December, adding the two line items comes out to 23.6 trillion ISK in ratting income. The RegionStats.csv file in the MER comes out to 22.8 trillion ISK.
Bounty income is heavily skewed toward null sec, as seen in the below chart.
Yes, players might expect a big decline in ratting income due to a major null sec war. But ratting income didn't decline for the first four months of the war. I'm pretty sure the latest EVE ecosystem dev blog is an indication CCP doesn't believe the war caused the drop in the ISK faucet.
The other fact that stuck out at me was the amount of destruction that occurred in null sec in December. Despite the largest titan fight in EVE history occurring on the last day of the year, the amount of destruction for the month was listed at 19.2 trillion ISK. The figure is the lowest amount for a month in 2020. More surprisingly, media reports indicate that in the first battle of M2-XFE, both sides lost a combined total of 22.1 trillion ISK. Meanwhile, in the RegionStats.csv file, the total losses in Delve in December were 3.2 billion ISK. Perhaps the losses will show up in the January 2021 MER.