I don't know why any marginal player in the NBA doesn't go to Europe.
because you can still make more money as a marginal NBA player, especially as you tack on years of experience (both in salary and union benefits after you retire). Now if you are GLeague level player, then it absolutely makes sense to go to Europe from a financial situation.
Historical Draft - Portland Trailblazers
PG - Magic Johnson, Tony Parker
SG - Clyde Drexler, Dennis Johnson, Alvin Robertson
SF - James Worthy, Alex English
PF - Charles Barkley, Ben Wallace
C - Moses Malone, George Mikan, Brad Daugherty