Genuine question: am I just a crap fishkeeper?

I would say that around HALF of the fish I bring home from my LFS don't make it past the two-month mark. The store is clean and the fishes appear healthy when I buy them. I feed high-quality food daily, (sometimes skip a day or two which I am working to correct), my tanks are fully cycled, water is clean (nitrates under 15 ppm always), light and heat are good. I do my research on the fish's care needs. I can keep platies alive, guppies, kuhli loaches, harlequin rasboras, plenty of shrimp and snails, even some rummynose tetras, but my two thick-lipped gouramis and my two attempts at German Blue Rams died within two months. Even in environments that should have been perfect for them, they wasted away. I feel a bit garbage, frankly. Am I alone in this? Do your guys' fishes all survive or is this amount of die-off somehow normal? All I know is I'm going to focus on "easy"/beginner fishes since at least I won't kill those ones.