It's because we don't want to lay out $30 grand for a new car that's only marginally better than what we have now,
& almost guaranteed to break down, often spectacularly... and it's depreciating faster than a Ugandan money market.
There's nothing on the market now (in the US) comparable to my Vanagon Syncro, especially now that I have the turbodiesel in it.
Rust is the killer, I can change anything on these but I've never tackled floors and stuff.
Welding isn't rocket science either, you just need a decent MIG wire-feed (spend a little more here for a good name-brand machine).
Watch some Youtube videos. Put in some time practicing on scrap metal, getting progessively thinner.
When you get the machine dialed in for thin sheetmetal without blowing through it, you can tackle your floorboards.
I had a cheap Harbor Freight welder, and it was miserable, couldn't turn it down enough to keep from blowing thru sheet metal.
I then got a used 120V small Lincoln wire-feed, it made me into a real welder, after some practice.
You don't need the gas bottle either, just use flux-core wire, and keep the tip close to the work.
My first efforts were pretty hideous... see the U-bolt weld to the muffler:

By the end of the afternoon I was laying down beads like this: