Rising Costs, Changing Audience
Google is a corporation and needs to increase their revenues. Their number one money maker is Google Ads, so one should expect inherit increases in average costs because of this. Additionally, their reach is ever increasing, meaning that there is more to manage than just ads on their front page; you have Google search results pages, YouTube, multiple partner networks, mobile apps, and many other properties.
While costs rise, Google makes it easier to advertise with them. However, without a thought out plan following best practices and targeting the right audiences and platforms, most advertisers do not achieve their goals and objectives.