MOV is a video container format which has nothing to do with the final file size. The thing that makes your MOV file large is the media data inside the capsule. A MOV can hold video data encoded by the advanced lossy codec like HEVC and H.264, the lossless codecs like Motion JPEG, and the low compression efficient codecs like Apple ProRes and Cinepak. Since the big file size is one of the key features of the latter two codecs, it's no surprise your MOV file is bulky.