Does a good economy means low turnout

[Agonized-Statism]

Not really. There was a cultural turn toward apathy in bourgeois democracy after the zenith of student activism in 1968. The counterculture, already falling into COINTELPRO-facilitated infighting, took a turn toward violent direct action after Nixon took office that alienated its last white middle class sympathizers. The development of a youth culture focused on self-fulfillment over collective action, such that the 1970s were dubbed the "Me Decade", was punctuated by a widespread distrust of elected officials after Watergate. It became uncool to stump for candidates and a hopeless endeavor even if you cared. You were either unapologetically hedonistic and focused on your own life (sex, drugs, and rock n' roll), or you joined a left-wing organization with a scarily long acronym and hijacked planes for your daily dose of politics. But no one was getting Clean for Gene anymore, that was nerd stuff. Contrary to your point, it was the "magic economy" of the 1960s in part that had enabled such widespread social experimentation and political cause-championing. The inward turn of the 1970s was helped along by the piddling economy.

This political apathy crested among the young in the 1990s, as others mentioned, with the techno-optimist neoliberal determinism of the "End of History". The DLC took over the Democrats and alienated the student and minority-led social movements, who were already considered a dying breed as the last of the baby boomers left college in the late '80s- the boomer-led student Anti-Apartheid Movement was the last big cause of note before Gen X took the reins, taking postmodernism to its logical conclusion of a nihilistic skepticism of any sort of political cause. Capitalism triumphed in the 1990s such that it had co-opted anti-capitalism and turned it into another branded individualist subculture. Bush and Gore were considered Tweedle Dee and Tweedle Dum, and not voting at all was considered the most politically enlightened move. Think the bell curve IQ meme. It's telling that this forum was started by a literal computer geek and populated by similar types concerned more with the data, statistics, and little factoids than an actual passion for politics in its early years.

Once again, continued voter apathy through the sputtering post-dot com boom economy of the 2000s and the sluggish post-Great Recession economy of the 2010s disproves the correlation between high turnout and a bad economy. Turnout started picking up when the fermenting post-neoliberal politics of the early 2010s, first present in Obama's pseudo-progressive 2008 campaign, boiled over electorally in 2016. All this being said, the dip in turnout can be attributed more to post-'60s individualist culture, and the recent increase corresponds with the post-Great Recession disavowal of that individualism as the source of voters' problems.