Pre-haskala, there was not a drive to make everything more stringent with time. So to that extent, I agree with Bizbody. Where is it written that halachic interpretations should become more machmir with time, or that restrictive minhagim should multiply with time? It has only happened in reaction to haskala.
ZD, as well as the civil rights movement, multiculturalism, which made it OK to stress one’s cultural differences, and the shift toward greater interest in traditional religions in the 80s, both probably contributed to the rise of charedim in the US (the MO benefited too).