mankind has been extremely lucky with our environments, among others:
- Jupiter & Saturn pick out most of the comets, so we encounter massive reset only very rarely
- thanx to hitting other planet long time ago, we have a spinning molten metal core inside planet generating magnetic shield for all nasty radiation
- moon gives us tides & stability
- our sun is just the right size and age to be stable
- we're located at quiet part of the galaxy, which itself is pretty stable
I think some primitive life (ie stromatolytes equivalent) can exist on many places, simply because it happened on our planet very early when it was very violent place to be - so random arrangement of matter into self-reproduction is feasible.
But to evolve into specialized multi-cellular organisms took more than billion of years, a step that might not happen at all.
And to create an intelligent life is another massive step up (or accident). There is Drake equation to manifest it, but basically all variables in it can be anything including 0, so it's kind of useless.
So from my perspective there are couple of options:
- universe is too young (if you consider average star age compared to estimated universe age), so we're one of the first sentient arrivals, others are behind in evolution
- we're just not interesting enough to be contacted by superior races - just look at the news, I wouldn't blame them. We're 'meh' category at best, although most like to think of themselves in very different perspective
- we're fucking alone, weird random anomaly (by far the most scary option of them all)
There is a wonderful TV series from BBC called Earth: Power of the Planet, which explores this topic to great details, highly recommended!