Over here in Ye Olde Worlde, van models also have very long lifespans, although they are replaced every 10-15 years or so. Vans are expected to be utilitarian and proven mechanicals are more important than handling or fashionable designs, so technology and designs don't age so much and margins are razor-thin, so investing in new models isn't very interesting.
That's exactly why we stuck with our vans for so very, very long. All they changed were things like door handles, headlights, grilles and so on, and of course interiors. We did the same with pickup trucks; Ford ran the same body style from 1980 to 1997! They put three different sets of hood, fenders, and headlight/grill package on it. From '80-86 is the Bullnose, '87-91 is Bricknose, and '92-96 F150 and & '92-97 F250/350 are called OBS, or Old Body Style. But really, they're all one body style, with two facelifts. If it ain't broke, don't fix it. Ford trucks of this era are generally some of the most-beloved vehicles in America, and they actually escaped to much of the world. I saw a bunch of OBS (&c;) Fords in Panama, for example.
What kept Ford going with their van for so very long is that the Ford Econoline with the 7.3 liter diesel was the absolute king of towing among vans, with 6,900 lb capacity. There was nothing else even close to that towing capacity with that much enclosed area until the second generation sprinter came out. It can be configured to tow 7,500 lb. The first-gen, however, only tows 5,000... there have been minivans which will do that (e.g. Chevrolet Astro.)