I just don't think this is particularly true. Here are some examples of conspiracy theorists and conspiracy theories associated with the left:

 - [Robert Kennedy, Jr.][1] (a longtime US Democratic Party personality who promotes conspiracy theories related to covid and vaccines)

 - [David Icke][2] (promotes anti-semitism and the lizard people conspiracy theory, associated with UK Greens and promoted by US lefties like Alice Walker)

 - Unscientific belief that people's health is harmed by nonionizing radiation, eating GMO food, chemtrails, or levels of ionizing radiation that are negligible compared to natural background. (Beliefs about GMOs led to the blocking and delaying of efforts to grow and distribute [golden rice][3], which could have prevented hundreds of thousands of cases of childhood blindness every year.)

 - Harassment and attempts to stop the development of sociobiology, such as the infamous incident in which a Marxist poured a pitcher of water over E. O. Wilson's head.

 - Denial of facts related to the Muslim world, such as denial of female genital mutilation. (Ayaan Hirsi Ali has written about this.)

Certain specific conspiracy theories are associated with the right, e.g., the birther conspiracy theory. That doesn't mean that all of them are.

Theories such as the birther theory and Icke's are racist, and one might imagine that this would lead to a correlation with conservatism, since there has been quite a bit of research statistically correlating conservative views with racism. However, it turns out that prejudice and intergroup bias, considered more generally, are actually not that correlated with ideology. See [Crawford and Brandt][4], Ideological (A)symmetries in prejudice and intergroup bias, 2010.

There is a 2019 paper by Douglas et al.,  "[Understanding Conspiracy Theories][5]," that has some discussion of this. Factors correlated with belief in conspiracy theories include:

 - "lower levels of intelligence"
 -  "alienation from the political system"
 - being a member of "low-status social groups" such as black people in the US
 - "lower levels of education and lower levels of income"
 - "most prevalent at the political extremes"

But, referring to a bunch of previous literature:


> There exists a strong assumption both within and outside academia that
> there is evidence for conservatives being more prone to conspiracy
> theories than liberals. Some studies support this assumption
> (Galliford & Furnham, 2017; Miller et al., 2016). Furthermore, several
> studies (e.g., Bruder et al., 2013; Grzesiak-Feldman & Irzycka, 2009;
> see also Richey, 2017) reported a link between conspiracy beliefs and
> right-wing authoritarianism—a dimension of political attitudes
> characterized by preference for conventionalism, authoritarian
> aggression, and authoritarian submission to authorities (Altemeyer,
> 1996). On the other hand, Oliver and Wood (2014a) and Uscinski and
> Parent (2014) did not find a link between political ideology/party and
> conspiracy belief, and Berinsky (2012) did not find a link between
> authoritarianism and conspiracy belief.

  [1]: https://en.wikipedia.org/wiki/Robert_F._Kennedy_Jr.
  [2]: https://en.wikipedia.org/wiki/David_Icke
  [3]: https://en.wikipedia.org/wiki/Golden_rice
  [4]: https://sci-hub.do/10.1016/j.cobeha.2019.11.007
  [5]: https://onlinelibrary.wiley.com/doi/full/10.1111/pops.12568