You got a remux, which is uncompressed. You can turn those off in Radarr to avoid those surprises.
If you want to fine-tune your file sizes (and quality) further, you can set up custom formats and quality profiles. The Trash Guides explain it well, the “HD Blu-ray + Web” profile on that page is a solid starting point. It’ll usually grab 6-12GB movies, but you can tweak it if you want them smaller.