All of the Lexus LXs and GXs sold in the US, why did they both have to be on the Toyota Land Cruiser platform? Why couldn't we have one of them be on Land Cruiser platform and then have the other be on the Sequoia platform? From my perspective, there is a difference between making a reliable SUV and building two vehicles that are nearly the same.
Basically they want to save money when they build things so they'll use the same platform for numerous vehicles it's more a monetary decision and manufacturing than anything else
The GX is based off of a landcruiser Prado 120, but the LX is based on a LC 100 or the newer 200 series I think. The LX is much bigger and has at least a thousand pounds over the GX. Some things to keep in mind, the Land Cruiser is no longer going to be made in the USA, They just never sold that many. That vehicle is a terrific off road beast, at home in places Like Australia and the like. In the US, most people are happier with the sequoia, as the size is nearly the same, and price tag is a lot less.
Soon the LX will be the only choice in the US for a true full size, luxurious Land cruiser, off road beast. Land cruisers are so big, they even have troop seating in some of them.
As Scotty mentioned, they use a lot of the same stuff for multiple vehicles. My GX470 shares tons of stuff with the 4runner, Tundra, and Sequoia!
The GX and LX may be similar, but it is similar to the difference in an explorer and expedition, or 4Runner and sequoia.