These "famous Belarusians" have some sort of strong connection to Belarus and its historical geographical area--even if that "connection" is only through the accident of the location of their birth. (Note: I use the term "Belarusian Culture" in its most inclusive possible meaning.)
Granted, some of these famous people are ethnically Polish, Russian, Lithuanian, and so forth, but their Polish, Russian, etc., biographies often refer to their having been born in Hrodna "Poland," Mensk "Russia," etc., often with never a mention of Belarus (or its rich traditions and language) in these biographies published in Poland, Russia, Lithuania, etc.
In my opinion, one must note that these places are and always have been in the Belarusian ethnographic region (see map), yet such mention on this A Belarus Miscellany Web site has resulted in outrage on the part of at least several (myopic) Polish and especially Russian/Soviet nationalists. . . . (I imagine most people do not share such chauvinist points of view.)
Most of the famous individuals listed here, of course, do have a very strong connection to Belarusian culture and its history, and such people are celebrated on this Web site (for their specific contributions to Belarusian culture and for their contributions to humanity in general).
(Note that on some of these Web sites, many of the spellings are transliterated from Belarusian or Russian, and that the expression "Famous Belarusians" is used in a very loose, inclusive sense--as I do here.