still can't use long tail keywords - what am i missing?

Most likely you're writing a separate page for every variation. Long tail mostly works the other way round: one solid page on the topic that naturally answers a lot of related questions, and Google ranks it for hundreds of phrases you never typed in. Look in Search Console at the queries an existing page already gets impressions for, then add sections that answer those properly. That's been far more reliable for me than chasing them one by one.