Except a or some astrological transitions over the years with effects. The simple answer is out of respect and because there is a cult following of 420. No not figure of the past the druggie scene. It's become almost a religion, this is our way to FU the degeneracy.
Simply other than respect, it's a mass mind, mass consciousness type of involvement. I'm sure one of the more prominent members can state we do it cause it's linked to a series of events since the involvement of the past nearing 100 years.
Other than that just our thing and those who revere figure of the past.