Because this is not 2010. Keywords are important, sure, but keyword stuffing is not. If you write a really good blog post on a certain topic, you will have automatically taken care of the necessary 1-2% keyword density for your seed keywords, I guarantee it. You will have done it without being all try-hard. Just pay attention to the few placements I have already mentioned: title, slug, a few headers/subheaders, the intro and the conclusion. The rest will happen naturally.