Aside from thrust/weight ratio, I suspect at least part of this conditioning came from a peculiarity with the Space Shuttle and its launch process.
The Space Shuttle's launch process was different because it had two different types of engines firing at launch. Its liquid-fueled main engines (mounted on the back of the orbiter itself) were ignited several seconds before t = 0. At this point, its thrust was less than its weight (and the whole stack was still bolted down to the pad!) so it did not move (well, not upward, at least.) At t = 0, its Solid Rocket Boosters(SRBs) were lit and the restraining bolt nuts were blown and then it started moving pretty much immediately, as its thrust was very quickly significantly larger than its weight once the SRBs started firing.
Falcon 9 has only one type of engine on its first stage and they all light at approximately the same time. As soon as they throttle up, the thrust very quickly becomes greater than the stack weight and the rocket starts moving.
Most rockets actually work more like the Falcon than the Space Shuttle, with all first stage engines being of the same type and ignited simultaneously. The Space Shuttle's mix of its liquid-fueled main engines and solid-fueled boosters in its first stage meant that the liquid-fueled engines would have to be ignited sooner than the SRBs in order to be throttled up and ready to balance out the pitching moment of the SRBs once they start firing.
By lighting them before the SRBs, it is also possible to shut down the liquid-fueled main engines and cancel the launch if something goes wrong during their ignition. Once the SRBs light, however, the rocket will go somewhere. If they light and the main engines are not functioning properly, the somewhere it goes will not be where you want it to go and you will not go to space today.
With Falcon 9, there are no SRBs to worry about. If one of the Merlin engines fails to light, they can just shut the others back down quickly and abort the launch. You will still probably not go to space today, but at least you still have a rocket (and payload) and can try again later.