How does gunpla? Is injection molded plastic parts that you can trim out of a tray and snap together. It's great fun if you want something to do with your hands that gives you a cool looking mecha you can pose on a shelf at the end of the process. Plus you got all different varieties and complexities to play around with.
Why is gunpla? Is because it's a fun hobby that you can do with your hands and doesn't require many tools. Also, Gundam was a TV show made to market toys to children, and as an adult with disposable income, I can confirm it's working.