This highly depends on your gear situation. Lets assume you just finished another pinnacle loot drop and got a chest piece much higher than the rest of all your current gear, but because you haven't gone up enough, your total light has stayed the same. (Like if all your gear is 1030, and the chest you earn is 1037) In this case the next drop pinnacle drop you earn will also be 1037, since drops are effected by your highest total power level. If you were to get a chest piece again from your strike pinnacle, you'd not up your power at all. Its likely due to a situation like that where your highest gear level was the drop you got, and thus wasn't beneficial to you. Its mostly a case of bad luck. If you want to avoid something like this from happening, there's a trick called back leveling, where hand in tokens/gunsmith materials, or doing lower valued powerful drops, to upgrade your other gear slots, so that when you do your pinnacle rewards, your less likely to get something that isn't helpful to you, so even if its in one of your higher leveled gear slots, you'll still get a stronger drop.

Your a -blam!-ing cheater