5e after a lifetime absence

I'm from the south so I'm not good with brevity, but I'll try. I haven't played since I was a kid back in the old 2e days. After a conversation with friends about games we loved as kids, I picked up the new PM in a bookstore and decided to give the game a shot as a grown-up.

Holy cow have things changed! I don't hate change, and I think it's a lot richer game than I played. The one change I truly don't understand is topping out at level 20. We used to play our characters forever, building a rich character over a long time. Now it seems the game is built to play disposable characters.

Is this accurate? Am I missing something in the switch from a slow build character to a quick level? Can someone help me understand what I'm missing?