Federal land. If you're really interested, the links are in my sig. The feds own ~85% of the state. If land bills hadn't passed in the '90s, there wouldn't be over 2,000,000 people in the Las Vegas Valley. The state had no need for land until rapid growth in the '90s left Las Vegas in the position we are now in up north.
Everything is built out here. Topography is as limiting as the feds. Most suburbs consist of small valleys, some tiny, that hold less than 10,000 people. The Mt. Rose corridor is built up from the valley floor almost to the summit. These are wealthy communities. These suburban areas are also well built out, but are mostly gated communities where the price of admission is in the multi-millions. The housing shortage isn't related to high-income suburbs.
Here's a photo from someone who hiked up Verdi Peak, which is just across the state line in California. It illustrates the housing issue.
The small patch of flat land center left is the town of Verdi, a suburb west of Reno. The area to the left of the freeway is developed. The area to the right is under construction. This is an old picture, but 1,200 acres of the foothills are now under construction with luxury homes. This will build out Verdi. The development, Quilici Ranch, borders on Forest Service land and the Mt. Rose Wilderness. Nowhere else to go.
Notice the topography. Homes are built up into the mountainside as far as they can practically be built. This is actually wide open space compared to parts of the North Valleys. Panther Valley may be a half square mile. Golden Valley may be a square mile and a half.
Anyway, there are limited infill projects and some, like the Quilici property, are building out the last remaining substantially sized parcels. With the growth of the Tahoe Reno Industrial Center east of Sparks, it would make sense to free up federal land between the two, which Rosen's bill addresses. The TRI Center employs over 20,000 people, all of whom commute. Building housing five miles away from work rather than 15 miles away makes sense to me, but politics doesn't always make sense.