I think that the low figures are due to the post-socialist "democratic" development of Bulgaria, there is no direct connection with the socialist era. During the last 20 years the active people lost their optimism, witnessing (and no participating in) relatively slow changes.
I would try to show my personal scale during the last years:
1990 rate 2 (empty shops)
1992 rate 8 (SDS governmet)
1994 rate 5
1996 rate 2 (bankrups)
1997 rate 5 (start SDS goverment)
1999 rate 7 
2001 rate 5 (end of SDS government, start of NDSV)
2005 rate 6
2008 rate 8 (before the start of the crisis)
2010 rate 6