The final straight section of on-ramps, just where or before where you merge with traffic on the highway is also known as the acceleration lane. You can read more about it here at the Federal Highway Administration Website.
The purpose is to give you space and time to get up to the same speed as the traffic flowing on the highway such that you can merge readily. Of course, if you want to to reach typical highway speeds of approximately 65 mph from the slow 25 mph when turning onto the on-ramp requires steady acceleration. This is aptly described in the CT Driver’s Manual (p. 36):
When you enter into traffic, try to enter at the same speed that traffic is moving. High-speed roadways generally have ramps to give you time to build up your speed. Use the ramp to reach the speed of other vehicles before you pull onto the road. Do not drive to the end of the ramp and stop or you will not have enough room to get up to the speed of traffic. Also, drivers behind you will not expect you to stop. If they are watching the traffic on the main road, you may be hit from the rear.
Alas, many drivers seem to be afraid to use that right pedal to get up to speed. As if they were thinking “Going fast is dangerous”. Well, it isn’t. The opposite is true. Of course you don’t want to be too fast. Just the right speed, namely the one on the highway. Otherwise you endanger yourself and others. By forcing yourself onto the highway at too low a speed you will force traffic on the highway to slow down for you. In Germany, it actually is illegal to force yourself onto the highway in that fashion.
Of course drivers on the highway can do something to help. Especially in dense traffic, it is a good habit for highway drivers, to move over the left to make it easier for entering traffic to merge. For the cars on the highway it is easier to merge left becasue they already are at highway speeds. This is particularly welcome at those rare on-ramps that have a stop sign at the end. If there is no acceleration lane, and if no-one moves over, entering traffic has a very hard time. Moving over makes their life easier and your life safer.