According to this article the problem seems mainly two fold, conductivity and thermal inertia (among other factors).
During washing temperatures get relatively hot (depending on the particular program chosen) to promote sterilization and help with cleaning.
Conductivity: Different utensils are made of different materials which will absorb this heat at different rates. Plastic has relatively low conductivity compared to say a metal pan or stainless steel object, thus gaining heat slower leading to less evaporation.
Thermal Inertia: Plastic objects are generally thinner and lighter, plastic is generally also less dense than other common kitchen materials, leading to retaining less heat, and conserving less energy, thus remaining warm for shorter periods, again promoting less evaporation.
There may also be other factors at work; such as surface properties of plastics like roughness or hydrophobia, which may cause water droplets stick more to its surface, or evaporate slower.
Briefly open the door
I have recently developed a practice that I feel helps getting most items (even plastics) almost dry.
After the cycles finishes, (the sooner the better so that the least amount of heat is lost), immediately turn off the dish washer and open the door.
Leave it open for a few brief seconds, long enough to let most vapor escape, but short enough that the minimum amount of heat is lost.
After that close the door again and let it sit for a while, no need to shut it, leaving it ajar will suffice. Ten to twenty minutes is probably more than enough if you are in a hurry; otherwise just let it sit for as long as you like after that.
This will ensure a lot of the humidity will leave the compartment while remaining warm, promoting quicker evaporation, ensuring that most items will be either almost dry or have a minimum amount of water when you return to unload the dishwasher.
Shake Plastic Items
One other thing you may do in parallel to previous procedure, (which can be more of a hassle to accomplish), is after opening the door while waiting for the steam to escape, individually grab any plastic objects and one by one give them a vigorously shake to loosen any droplets on its surface.
If your ratio of plastics to other materials is anything like mine those should be a minority, so it should be quick; one or two shakes per item is generally enough. Just let them splash into the sink, or even back into the dishwasher to get most of the surface water off; then put them back in and close the door again. The remaining heat should take care of most remaining residual humidity.
As mentioned in the comments, if you have no delicate items that might break, you can also just give the whole rack a shake instead. Items with intricate designs or crevices that pool water may still benefit from a good individual shake though.