The article mentions that there were 902 players on Opening Day rosters. It also shows payroll for all teams.
So I added all that up ($3,825,147,026) and divided by 902 and got $4.24 million. I don't know why there is a difference.
The article also mentions "the average likely was lowered slightly by the expansion of active rosters to 26, which probably caused teams to add 30 players making near the $570,500 minimum."
I multiplied 30 times $570,500 and got $17,115,000. Then I subtracted that from the total payroll of $3,825,147,026. That left $3,808,032,026. That is total payroll without the one extra player (at a low salary) on each team.
Taking those guys out leaves 872 players. Then $3,808,032,026/872 gives us an average salary of about $4.37 million.
That is about 3% higher than the $4.24 million I got above. So if salaries are down 4.8% since 2019, then perhaps most of it is due to the extra players with low salaries being added in to the mix. The extra players might be having more than a slight effect.
Now the article did say the extra players made "near the $570,500 minimum." Maybe a few of the extras made more than that, so the affect might not be so big. But my guess is that it matters quite a bit.
The article mentions some particular cases of players with high salaries not making a roster, which lowered the average. Also, "The 50 highest-paid players are getting 33.4% of all salaries, up from 28.6% in 2017, and the 100 highest-paid are receiving 52.4%, an increase from 42.5% in 2017."
This reminds me of the book Can You Outsmart an Economist? by Steven Landsburg on the "stagnation" of incomes. He points out that for all sub-groups, incomes rose quite a bit over time. But more low income people joined the labor force, so it drags the overall average down and makes it look like wages or incomes stagnated, like in this case for baseball.
This table from Landsburg's book shows that from 1980-2005, all 4 groups (white men, nonwhite
men, white women and nonwhite women) had increases in median income
(adjusted for inflation) of at least 15% while the overall gain was just
The reason is that the lower paying groups grew more than the higher paying groups, keeping the average increase low.