Why can't clicking the logo do both depending if you are logged in or not
Sites that direct to a dashboard usually do it because they have one!
Not all sites that you have to log into need a user centric dashboard, and if that is actually somewhere to go to manage your account, and not to 'use' the site then it should be a secondary action.
I log into Amazon and see a tailored version of the homepage (offers for me) but I would not say it was my dashboard because that is in my account page.
Amazon does not want me distracted into looking at previous bills etc when I came to the site to buy something.
If a lot of the content is available to users that are not logged in then often the logged in user still needs or wants to browse the landing page and all its content, only doing something user centric when they need to amend the content in some way, or enquire about a product (e.g. eBay)
On the other hand, something like Highrise (a CRM application), or Trello when I log in, the only thing I care about is my own dashboard with leads that I need to follow up etc.
So, it really does depend on your use case.