For the 2020 tax year, you pay 0% on long-term capital gains if you have total income of $40,000 or less; 15% if you have income of $441,450 or less; and 20% if your income is greater than $441,450.
Interesting, I never paid attention to that. I would guess the number of singles/couples earning $40k/$80k total per year or less and own enough stock to get material dividend income must be miniscule.
Lots of retired affluent people fall into that category. A $4M portfolio would throw off $80K in annual dividends assuming an average 2% dividend rate.
A retired couple with $4M net worth excluding home value is 97th percentile. $1M is 90th percentile.
And they surely would have a significant proportion of assets in bonds yielding a couple percent rather than stocks, so earning tens of thousands in only dividend income is probably super rare.