Like most things having to do with, SEO this isn’t a simple answer. My first question is, where are you getting your zero search volume results data from?
With the exception of Bing, almost every keyword research tool out there provides you with data that’s pulled from Google Ads. What That’s decidedly different than being able to access actual organic search volumes for any keywords. Google doesn’t provide that data, so most of the tools you’re using to get search volumes are providing search volumes for paid keyword searches done on Google. So while the data you see can be directional and help you in picking out keywords, it’s not 100% accurate.
Put more plainly, if a keyword search didn’t generate at least 1 paid ad from Google, then for purposes of this discussion it had zero search volume.
I just did an experiment. Using a tool I love called KeywordKeg and the term “marijuana” as a seed keyword, I found 1,246 different variants I could optimize for. The phrase “how would marijuana increase tax revenue” shows no search volume at all. I get the same non-result for “top marijuana stocks 2020” but common sense tells me that couldn’t possibly be accurate.
So sometimes, if your keyword expansion list shows up with zero search volume for a keyword and you’ve got a gut feeling that that number is wrong, it doesn’t mean you should ignore it. Go with your gut. Just remember that the keyword research tools you’re using are not right 100% of the time.