Sen has literally been playing way before afreeca and they had to travel back and forth way too many times. Burn out can happen to any team. Geng has not played nearly as many off season matches as sen that too on the highest level. Edg was burnt out during afreeca just as sen is now
Teams are just a lot better now. You can't win with slackers against top teams like 100T, FNC, TH, PRX etc in this meta and SEN has too many slackers in the excuse of chemistry(the chem arg is cope btw).