'At's cause it actually had a comeback. Following the breakup of the Brotherhood of Eternal Love from about '74-'80 it was all garbage when there was any, at least here in CA, and reflected in High Times' "Market Reports". If it was pressed it was likely worthless, but blotter was least still pure, if weak.
My last trip with something man-made was in '82 after about an 8 year break, blotter, the hearsay was it as one of the original BEL chemists. Still much weaker dosing than what I experienced in '70 and '71 marketed as Orange Sunshine (which I believe, even though it is a mythical "brand name" but in retrospect it matched the descriptions of crudely pressed orange "barrels", as well as being on the south side end the SF Bay from where Scully and Sand originally operated) ) as well as "Window Pane", one of the earliest forms of blotter, when it would be mixed with gelatin and dried in sheets, then cut into squares.
https://belhistory.weebly.com/
My hypothesis is that quality took a severe hit after the DEA busted Scully and Sand, I also recall news a the time about early efforts to target "precursor" chemicals and suspect this may have also affected market quality of the period. Just recalled also cultivated psilocybin was just starting to come in, in some volume, ca '78. Maybe to fill the gap.
Also just recalled the mid-70's heralded the onset of the cocaine epidemic. For about 4 years there cocaine was actually easier to find than weed (remember the "Paraquat" scare?) and psychedelics were simply out of style and in low demand.