For me the fact that there was a long reign was a damge for the little families because the bosses prefer to don't made new members and after their dead the families was hitted by LE and quickly dead.

Cleveland family:Scalish era (1944–1976) the family come to his peak of 60 made men but Scalish doesn't made new blood but the family was damaged by danny greene war and the Lonardo and Zagaria flipping;
Bufalino family: Rosario Alberto "Russell" Bufalino (1959–1994) same thing but the family was more small,about 40 made men and was disbanded after Billy D'elia flipping;
New Orleans crime family:Carlos Marcello (1947–1993) Marcello keep his political connection for him and take it in the grave
Pittsburgh crime family: after the LaRocca reign (1956-1984) when chucky porter was made in 1986 he was the younger in the family (and porter was 50 y old at the time)
and so on.