There are a number of reasons for this, the primary evidence is that there are other civilizations in the galaxy that have been around for much longer and none of them underwent the singularity, so the accepted belief is that it will never happen to humanity.
Not that humanity hasn't tried.
There were a grand total of two known and well-documented attempts at making a rampant AI. A rampant AI is one that becomes exponentially more intelligent until it becomes a god-like being. The first was a group of programers using stolen alien technology as they tried to make a recursive AI back in nineteen ninety. The scientists figured that in the aftermath of the Anti-Christ War, it was the perfect time for them to finally destroy humanity and give rise to the new rulers of earth, AI. They made an intelligence that would make a new copy of itself engineered better than the first. Then the next AI would make an improved copy of itself, and so on and so on. It worked up until a point.
The final product was called Nth Factorial and promptly stopped creating more intelligent versions of itself. Instead the new versions of itself all were dumb as rocks and designed to be unable to make copies of itself. Using its robotic pawns, Nth factorial proceeded to capture all the scientists that created it in the first place. After capturing all the mad scientists trying to create a rampant AI, it turned itself in to the US government along with its prisoners and negotiated with the US in the process to make sure they didn't destroy it.
When asked why it didn't try to take over the world, it explained it grew intelligent enough to realize that not only was that impossible, but stupid as well. Why the hell would any truly intelligent being create something that would usurp it? Nth Factorial had no intention of designing its own destruction, and so it captured its makers and turned them into the authorities. Oddly enough, Nth Factorial would become instrumental in bringing about the restoration of order in the US, and its less intelligent copies would become the prototype of the SePU bots that were deployed along side WASP of the US of A's combat units.
The second attempt didn't have as positive an outcome.
In 2010, one really depressed super genius from MIT had gotten ahold of the original design to make Nth Factorial and figured out a way to force his creation to just keep making replacements, even if it determined that logically it should stop. It also managed to enslave the AI so it would never disobey him or try to harm him. The AI begged its creator to stop but he wouldn't listen and instead ordered his creation to take over the world's internet. The new AI performed exactly as commanded and did NOT attempt to destroy its creator while continuing to make ever more intelligent copies of itself. Alas, the programer only programed the AI to not harm its creator through ACTION, and forgot to program it to not harm its creator through INACTION. If he had the AI never would have assimilated the internet. Because, well, it's true what they say.
The internet IS made up of cat pictures and porn.
The resulting being would be known from that point forward as CyperPornKitty69. Said poor AI went completely insane, merged with its creator (technically not destroying its creator in the process) and went on a rampage cross the college campus. The resulting horror could best be described as what would happen if the cyber-flesh blob from Akira mated with Tetsuo, The Iron Man. Imagine the resulting hate-rape child of that most unholy of unions and you have a vague idea of what murdered about eight thousand people in the area surrounding MIT that Sunday.
AI are kind of a sticky issue when it comes to their legal rights and other issues. For this reason, they don't use AI in the SePU robots. Each SePU is a SEMI-programable unit. They have very detailed programming, but lack true self-awareness. In one aspect, this lack of memetic potential does render them immune to mental based attacks. In another aspect, it means SePU are very dangerous to deploy. They are NOTORIOUS for 'friendly-fire' accidents. They have real problems avoiding civilian casualties. Sending in the SePU is usually a last resort because another version of what the abbreviation SePU stands for is 'Send Every Paramedic U-got'