What is the thought-process of the Driver, who does not immediately accelerate on freeway onramps to match freeway speed?

Many drivers, when entering a freeway onramp, do not accelerate to a high speed. They accelerate all right… to about 55 mph… but why are they not entering the freeway at the speed of the drivers on the freeway? They think they are being “slow and safe” but are just being stupid and unsafe.

What is their reasoning? How can I empathize with them more?

Not talking about trucks and Volkswagens and the disabled, and those following another car here, they do not have a problem of will, but of ability