I’m not as familiar with Gatsby but just by reading through your log files it appears that a large portion of your build process requires generating assets from scratch as well as downloading binaries from source.
Support will probably have a better answer for why your build times are so long but my best guess is because a lot of compute-heavy commands need to run before the site is actually built and ready to go. One way to cut down on your build times would be to minimize the amount of operations done during a deploy and have the majority of the heavy lifting done before deployment so Netlifys build image doesn’t have to build your site from scratch for every deploy.
For more information, I recommend checking out this post: [Common Issue] How can I optimize my Netlify build time?