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. (a longtime US Democratic Party personality who promotes conspiracy theories related to covid and vaccines)
David Icke (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.
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 FGM. (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, Ideological (A)symmetries in prejudice and intergroup bias, 2010.