Because the existence of a Creator or not is the attempt to answer who, or what, made the physical universe the way it is. FSM is what? What question does it try to answer? It is stated by several scientists(not necesarily the majority) if some(I think 6) basic constants of physics didn't have the values they do, life would not emerge. See fine-tuned universe: http://en.wikipedia....-tuned_Universe. It's not hard to imagine; there are countless planets but only on Earth, as far as we know, life exists, because it just happens to have the right conditions. Taking that into cosmological state, why does it happen that the universe has those specific laws and right conditions that allow the emergence of life?
The problem is it doesn't attempt to answer anything; by invoking a creator you attempt to side step the issue by saying 'god did it, don't ask why or how because we can't understand him'. This is not an explaination, it is just hand waving and at that hand waving which then brings up the quesiton of 'ok, so how did a creator come into existance?' which is answered by yet more hand waving ('always existed', 'oh, exists outside space-time') and a side stepping of the issue again.
This is not explaining; this is fairy tales.
It would be much like if, when asked by a child, what makes the thunder and lightning during a storm you answered with 'god does it'. That is not an explaination. Now, at one point when humans didn't understand the processes involved it was considered an explaination, but these days if you tried to pass off that kind of thinking to a child then anyone over hearing it would react with horror at worst, distain at best, and the child in question would later suffer when in school he brought up such a thing and would promptly be laughted at by any child who knows the real reason.
During the 'early days' of humanities existance this would be a reoccuring pattern; encounter unknown thing, ascribe it to a 'god' or 'demon', cower in fear until technology allows us to understand it.
At one point planets and stars we consisdered gods and heroes; we know better. At one point illness was ascribed to the work of the devil or demons; we know better. At one point the earth was considered to be the centre of the universe; we now know that it exists in an ultimately unremarkable location.
And every time technology answers one question religion moves the goal posts or moves on to the next big question. The existance of the universe and ascribing it to a creator is nothing more than this; something which, when the concept of a creator was invented, was beyond our ability to understand and thus ascribed to a bigger more powerful being.
Fortunately, like every other thing religion 'explained' before, there are people there are people working to understand the REAL why rather than answering it with hand waving and mumblings about an 'all powerful' being. Without those people, those willing to question, well if we still existed at all then we'd probably still be living in caves, scared of fire and wondering why the demons have seen fit to make our arms go this smell green colour...
As for 'the tuned universe' theory... well, it is just that 'a theory', a thought experiment and one which meshes nicely still with the idea that this isn't the only universe to ever have existed. I only skimmed the article as I'm at work but I've some passing familuarity with it; it only looks like something set the universe up correctly if you consider that either a) this is the only unverise to have existed and/or b) that the universe was 'created' for humans to adapt to in our current state.
Consideration (a) doesn't hold if you consider a reality where by this is one of a series of universes to have happened one after each other. In which case feedback from one to the other got to the point where the 'constants' allows for us to evolve into. (This might also explain the lack of uniformity in the CMB of the universe; if one is seeding another there is a chance this feedback would result in a
Consideration (b) ignores the realities of evolution and how life would come about. If the physical constants were different then life would be different or not exist; the former allows for the questioning of the state of the universe and the latter naturally unquestionining.
The idea that there are 'countless planets but only one earth' is an egotistical take on human existance. As already noted there is nothing 'special' about the place of our solar system in the universe and given how mind bogglingly big the galaxy is, never mind the universe, it is more than likely that there are other life carrying planets out there. We haven't detected them yet simply because our technology isn't good enough yet (but its getting better with every passing year), however at the same time we have found evidence which points to the idea that simple life could have existed on Mars in the distant past and we've also discovered organic carbon inside metorites carried to earth.
The fact we haven't detected life yet does not disprove it's existance; much like not knowing that bacteria existed didn't stop them from doing so and making us sick.
I very much doubt you'd find a scientist alive who would say 'we know all the answers!'; science is a constant quest to find out more after all. However, at the same time, just because we don't have the answers now doesn't magic the hand waving any more 'right' either.