Everyone knows, or should know, that hosting a party involves a lot of work, cleaning, food preparation, getting dressed. Expecting a host or hostess to drive over and pick you up isn't just rude, or entitled, it is an incredible imposition. If someone is adult enough to be invited to a party, they are adult enough to provide for their own transportation.
If this happens with younger adults, perhaps they were raised in homes where they were allowed to believe that the world revolves around them. There are parents who cater to their kids, and I imagine that when they grow up, these kids might think that expecting a host to get in the car and come to get them is reasonable. This is why it is important to say "no" to people. Every time that a person makes an unreasonable request, and we don't kindly say "no", we are letting them think that imposing on people is acceptable. We are encouraging them to be self-centered.
When a lot of us were in our early twenties, we made some missteps, usually due to lack of experience. I believe that in the past people were more likely to let us know when we crossed the line. I think that now, a lot of people are so afraid of hurting someone's feelings that they unintentionally encourage poor behavior.