Per 50 million, ranked highest to lowest
North America
United States + Canada
Total population of the region: 369,580,385
Divided by 50 million: 7.39
Playerbase: 1,511,378
Playerbase per 50 million people: 204,516
Korea
Korea
Total population of the region: 51,709,098
Playerbase: 153,392
Playerbase per 50 million people: 148,322
Korea formula given in comments
Brazil
Brazil
Total population of the region: 210,147,125
Divided by 50 million: 4.20
Playerbase: 511,834
Playerbase per 50 million people: 121,865
EMEA
Europe + CIS + Turkey + MENA
Total population of the region: 1,568,605,016
Divided by 50 million: 31.37
Playerbase: 2,582,332
Playerbase per 50 million people: 82,319
Asia-Pacific
Southeast Asia + Oceania + Japan + South Asia
Total population of the region: 2,723,095,454
Divided by 50 million: 54.46
Playerbase: 2,518,186
Playerbase per 50 million people: 46,239
Latin America
Central America + South America + Caribbean
Total population of the region: 660,707,451
Divided by 50 million: 13.21
Playerbase: 483,210
Playerbase per 50 million people: 36,579
Keep in mind that EMEA and APAC are so big and many of the countries that are included are not as developed as NA. So it may be slightly misleading.
On the flipside, Korea might be much further developed and have better tech access, so take this with a grain of salt.
Formula:
The population of a region: r
population of a region: 50 f
playerbase: p
playerbase per 50 million people: m
r divided by 5,000,000 = f
p divided by f = m
m = playerbase per 50 million