The real reason is they couldn't get OLED to work on a larger screen, Samsung went RGB OLED which had huge problems with blue pixel lifespan and total pixel failures, I'm sure somthing like 70% of the screens that came off the line were unusable. Where as LG went for RGBW OLED technology all white OLEDs with a colour filter over the top which solved the blue pixel problems and the pixel failures
http://flatpanelshd.com/news.php?subaction=showfull&id=1474618766
it's a real shame Samsung couldn't get RGB OLED to work because that screen was absolutely perfect and would have given a DSE,Banding,haloing free and perfect viewing angle tv every time
http://www.hdtvtest.co.uk/news/ke55s9c-201310273395.htm