You missed one factor - How much money Google wants to make - because no matter how much Google lies about it and people buy the lies quality score very often is just a sham to justify charging more for placement even in niches where there is no competition that would run the bids up.

Hi blitz20,


First, you need to understand what Quality Scores are and how they are calculated.
(Source: Check and understand Quality Score - AdWords Help )

It is no accident that the first 3 methods listed as factors of your Quality Scores are based on CTR. Your Click through rates are the single biggest factor, making up about 65% of your Quality Score.

Here are the most important things you need to do to improve your Quality Scores:

Account Structure - Learn how account structure impacts your CTR and thus your Quality Scores. Organize your account with themes, create separate campaigns for each product/service category of your website, and use tightly focused themes for each ad group, and write ads for those specific ad group keywords. Split your campaigns into individual Search and Display campaigns and use different methods to target those different networks.

Ad Text - Write ads that get high click-through-rates using relevant and attention grabbing headlines, relevant and compelling value propositions, and include a CTA (Call-To-Action). Be as specific as possible, avoid using general or ambiguous statements.

Landing Pages - Select the most relevant landing page for each ad, and make sure that the value promoted in you ad text is easily found on your landing page.