What's so unbelievable about life developing on only one out of 9 planets? 9 isn't a very big number! ... Consider the extraordinary number of planets out there, and 9 is nothing!
Life isn't going to develop on every single planet, just as here on our own planet life (or at least, life beyond the most basic stages) does not develop in every single environment. There are conditions that must be met.
Using our own solar system as an example of the entire universe is "bad". It's like, looking at a volcano and using it as an example of how life must be on the entire planet. It may be that our solar system, in relation to the rest of the universe and other solar systems, is a fairly uninhabitable one, and we just happen to be one planet in this "relatively uninhabitable" system that was able to meet certain conditions appropriately. Yet many other systems may be filled with life on multiple planets. We simply don't know, and we can't presume to know from simply looking at our tiny, tiny, tiny little "corner of the world". It is not a very accurate "sample set". It's like trying to study the entire population of the world, by studying only one person -- or even less, by studying one person's thumb.
Even if our own solar system was representative of how life is "laid out" among other systems, if only 1 or 2 planets within each solar system have life, then when you look at the "big picture", that's still a LOT of life "out there", and suddenly our "one out of nine" doesn't look that rare.
Or, if our solar system is used as a percentage representation of all planets in the entire universe, that is a little over 10% of all planets that would have life. Out of billions and billions of planets, 10% is nothing to scoff at.
But, we aren't even capable of exploring our own solar system to any great extent, so how can even it be used as a sample set? There may yet be undiscovered life, in various stages, within our own solar system. To say that life has only developed on "one out of nine" is merely an assumption based on an extremely limited data set. Yet even if "one out of nine" IS an accurate representation of "intelligent life" across the universe, like I said that's still a lot, and with plenty of room to grow!