On steemit we have the opportunity to share our posts on other social media platforms and generate our own traffic and our own following, but steemit is not being used that way.

I share all my posts in my other social media networks and bring traffic to steemit like that since 1.5 years and I know that a lot of others are doing the same. Why do you believe that doesn't happen here?

Why should steemit provide new accounts with more visibility? (...) its not steemits responsibility to provide marketing or traffic to YOUR content.

Who are you talking about when you say steemit? @steemit or Steemit Inc or the community?
In general we're all responsible for our own doings, no doubt about that. Still if a company advertises with claims such as Money talks or Your voice is worth something then this roots certain expectations. I've been working in marketing and sales for 12 years now, and the number one rule I've learned in all the companies I've been working for is:

Don't ever lie to your customers.

Are we true to ourselves if we advertise steemit using the word money? There's a huge gap between message and reality, and that's why we have only 12% user retention. That's my personal theory.

How many steemit inc staff accounts are part of a voting circle and what I would call - self supply?

I have absolutely no idea. Why don't you ask them? :-)