Affiliate marketing is alive and kicking!
The real truth is that it's a lot harder than it used to be. In the past you could have opened a crappy website and relatively easily manipulate Google to rank high for many keywords.
Adwords was also a viable option but now clicks are more expensive and you have to make sure your landing page isn't a bridge page (a page that adds no value to users except sending them to the vendor)
To be a successful affiliate in this day an age you need to create a website that actually makes visitors happy, you need to have great content and you need to be active on social media.
This is why a lot of people who are seeking quick and dirty money get frustrated with affiliate marketing very quickly.
If you have the patience and plan on building a great website, affiliate marketing is definitely one of the best ways to monetize your site.