I studied with a lot of said scientists for my physics degree and I don't know that this is necessarily true. For one because scientists rarely agree on anything unless it is basically certain.
A good mathematician appreciates that you can't draw any conclusions at all with a sample size of one. And they also appreciate that human beings are exceedingly bad at intuiting probabilities - like crazy bad at it to the extent there are a bunch of fallacies all based on how bad we are at judging probability. It could very well be the case that as vast and unimaginable as our universe is, the probability of life and/or intelligent life could be equally unimaginably small, and maybe even smaller. The chance of dealing a deck of 52 cards in a specific order is roughly equal to selecting a single atom at random out of our entire observable universe. What if the mechanism that creates life looks like that?
It's the anthropic principle in action. It feels unlikely to us because we are here, but if we weren't here then we wouldn't even be around to ask the question in the first place. Imagine two universes, one with life all over the place that we haven't bumped into yet, and one where it is just us. We could reasonably be in either one of these universes and we would still ask ourselves the same questions, and we would all be on this thread citing "surely there has to be life elsewhere". Our own existence gives us zero information about the prevalence of existence itself.