About the reasons, I apologize for my English:
1) Sciostakovich n.15
Great, even if not supreme, achievemente by an undisputed master in serious illness, always in touch with audience
2) Rautavaara n.3 (but I could have listed almost as well n.6, 7 or

Great capability, after more "modern" experiences, to rework past languages in an idiom aiming to audiences
3) Tippett n.3
Grat freedom and indipendence of idiom , very strong personality, asking much, but not the impossible, to the listener).
(Other contenders: Sallinen, Weinberg, Bernstein, Arnold, Simpson, Schnittke).