When people started realising how bad smoking was in the 50's, the tobacco companies started manufacturing filtered cigarettes, which had the appearance of being less harmful. They even added extra chemicals to make used filters appear darker than they otherwise would, so that they appeared to be filtering more effectively [3].
[1] https://pubmed.ncbi.nlm.nih.gov/9241071/
Lots of people also forgo a roach altogether because they “want to taste the resin on their lips.” - Martyjuana’s words, not mine. But I agree.
A roachless joint is actually the recommended method of consumption by Ganjiers for cannabis flavor assessment.