〜わけではない

わけではない denies a conclusion someone might draw, without denying everything: 肉が嫌いなわけではないが、あまり食べない, "it's not that I dislike meat, I just don't eat much of it".

It softens and corrects. It's common after a sentence that might be misunderstood, and often followed by が or けど and the real reason.

With words like みんな, いつも or 全部, it means "not all" or "not always": 日本人がみんな寿司を好きなわけではない, "not all Japanese people like sushi".

というわけではない is common after a whole idea: 高ければいいというわけではない, "expensive doesn't automatically mean good". In speech, it's わけじゃない.