How long have you got?
On the one hand: It is used in professional fields, just not to the same degree as other applications. As well as starting as an internal project with a ‘professional’ organisation, I, along with many other members of this website, use Blender professionally. Problem is, that certain applications have a foot hold in certain industries - Lightwave / Maya in cinema, Max in games etc. (not totally and absolutely, just greater percentage)
On the other hand: There are lots of reasons why it does not see greater use, and most of them are all about education, not lack of capabilities (now or potential).
i. You get what you pay for. An adage that is common across all ‘free’ software’ (not just Blender) is that many companies believe that they get what they pay for - hence, why most companies use MSOffice rather than OpenOffice. Things gradually change as companies have to justify expense, but that will probably not happen in the Graphics world as a lot of money can be made that offsets the cost of licensing.
ii. Training. Companies can pay for training for their employees, as well as many already having training out of colleges and universities. Blender training and education is still in its infancy. On top of this, companies that produce applications for sale also often sponsor training environments. My local college for example has a course on 3D Design (not necessarily CG) and use Maya for that process - despite everything that I’ve heard saying that Maya does not have a particularly good modeler and caused the Lighwave > Maya pipeline to develop (what I heard, don’t quote me on that).
iii. Exposure. Despite the great work that ED and lots of others do with Blender (don’t just fixate on ED), Blender still does not have the visibility of ‘professional level’ and ‘professional length’ animations etc. I seem to recall that in the last two Expose’s for example, there is no work credited to Blender (though I seem recall from reading on this site, that there is at least 1 in Expose 4).
iv. Development. Blender, until recently, was still in its infancy. There are lots of additional functions over and above the basic 3D mesh building that are needed in a professional application. In other applications, these are provided by plugins and other applications - many produced by third-parties, and nearly also needing their own licenses (i.e. more expense). That has been gradually changing in Blender, and it’s now out of its diapers. Many of these plugin equivilents are now available.
TBH. The above are just a few reasons, but they are all changing. What is required is more education of buyers, more visibility of Blender with professional quality work, and more options for ‘official’ Blender training.
It will come - and that’s the view of a company owner / professional artist, not just a ‘Blender Believer’.
Blender has the makings of a world-class CGI application and its probably already 90% of the way there - we just need to convince the rest of the CGI world of that.