I know to some it is a "lifestyle". I know some who own two lots in two different areas and spend six months or so in each place living in an RV. That is full timing. I know some who follow a dream, like following NASCAR around the country. Others are able to visit their children around the country. I know one couple that spends six months in a 'resort' in southern California and the other six months traveling.
To me it is about the ability to travel. I want to travel the back roads and visit as many parks as I can, especially those with waterfalls. To me the RV is not a lifestyle, it is a Mode. There are many ways to travel. Some are restricted by money and some by how much you can carry with you.
I spent over six months looking until I found just what I wanted and made a good deal. I filled its nooks and crannies with the "stuff" I call my life and took off. Some people think of my Rig as a traveling camera store or museum.
My point is that there is no one reason to full time. Frankly, if I was going to spend my life in one place, such as near Yellowstone National Park, I'd own a house. There are creature comforts that come with a house that are nice. I think I would install two 60 gallon hot water heaters so I could stand in a hot shower for an hour if I wanted. I'd have one room, a large one, set aside just to hold my camera equipment. I'd have a little bug of a car that got 50 MPG and I'd travel into the park day after day. There is enough there to keep me busy for the next fifteen years or so.
But, for about seven months out of the year it is a bit cold there to do what I want. And, as nice as Yellowstone is, and it is wonderful, so is Arches NM in Utah, Rocky Mountain NP in Colorado, Glacier NP in Montana, most of Arizona...and Nevada...and Oregon. Don't get me started on Oregon. There are three entirely different ecosystems in Oregon and all are nice to walk and photograph. But, it gets cold there too. That leads me to Big Bend in south Texas. That is a great place to summer. And what about fall? How about Maine and the White Mountains of New Hampshire? You can spend weeks following fall color south.
You mention Spring? You just have to see the Bob Marshall Wilderness burst forth with wild flowers each June. Just as fall starts in the north and moves south, spring starts in the south and moves north. Spring comes late in Montana, but in coming late, it kind of explodes onto the scene. It is not as subtle as spring in the south. It is compressed and intense. One day it is white with snow, then it is brown with old groth, then suddenly green and suddenly all the colors of the rainbow. Not many parks are known by a nickname, but if you Google 'The Bob' it will be listed in the top ten.
So full timing is different for everyone. It is the only mode I know of that will allow me, on a budget, to see the places I want to see. I know many of you live more or less full time in an RV and for reasons of your own you don't move around much. That's fine. It works for you. But sometimes I get that itch and I just gotta go. I guess it is like the food cravings a pregnant lady can have. I am told there are times when nothing in the world is more important than eating strawberry ice-cream using a Hershey Bar as a an edible spoon. I get that way with places, like Baxter State Park in Maine.
So, if you are a full timer, you know why. Just don't forget something very important. They put wheels on these rigs for a reason. And don't forget the "R" in RV stands for Recreation!