You'll find intricate trusses and structures reproduced. There are major advantages to using laser-cut paper. One is that we can apply lithography and metal-foil bonding techniques, making sure all the proper colors and details are present in your kit, without your having to paint them in. Another advantage is that the parts can be labeled for your convenience in assembly. The glue is non-toxic.
Paper is a relatively easy material to work with.
Also, paper products are perfectly suited for fast delivery by first class mail. And for clubs or other groups. There's a price break for ten or more of most kits. The Keck Telescope and the Apollo Model are exceptions. The new, simpler, smaller Mars Polar Lander kit can be assembled in an hour or two at most.