Popular? Toyota sells 150k
Popular? Toyota sells 150k Tundras a year, a tiny fraction of the number of full sized pickups any of the Big 3 sell annually. A better question is why is it that Toyota's full sized trucks don't sell better. Particularly given Toyota's stellar reputation for reliability. The answer sadly it blame Toyota's accountants. Toyota has become an automaker where product planning isn't by engineers and designers burt rather conservative accountants. Tundra, Tacoma and 4Runner are all dinosaurs. The accountants' strategy is to minimize cost and squeeze out every Yen they can from existing models no matter how outdated (The 4Runner has a 5-speed, the Tundra a 6-speed. Very Y2K of them..) That's what the top price they can charge for a loaded Tundra barely hits the mid-point pricing of the line of any of the American brand competitors.
If Toyota returns to a company run by technologists and engineers rather than bean counters, I think they could come up with a competitive full sized truck. Thus far their position in the segment has been tenuous at best.
The low price due to Toyota's aging design and small market share in the segment is beneficial for those who want a well-equipped reliable truck at a very low (compared to similarly equipped alternatives) price. I'm tempted to replace my aging Ram 1500 with a Tundra TRD Pro off-road. Though the new Rams (and F-150s and Sierra/Silverado's) all have better interiors, better comfort features, etc. than the Tundra, if you have an old Big 3 truck, you don't have those things and Toyota is selling a truck today that is similar in interior materials and features to the truck you have now, except that you do get Safety Sense, which is a useful suite of features for distance travelers. And you get it for about the same price you paid for your old truck when it was new, whereas buying a new Ram, F-150, etc., you'd be looking at paying $15k+ more than you paid 8-10 years ago for a given trim tier.
So Toyota's New Old Stock Tundra has a place in the market, but it's definitely NOT competitive and the comparative sales figures reflect that fact.