4K video files are tremendously large. The files are not larger than 4 GB which it is very normal for the camera to split the video files.
This is because most of the portable SD Card uses a specialized file system called "FAT32", which by nature cannot store files larger than 4 GB and it is the reason why files are spliced into 4 GB.
Although some SD Card uses "exFAT", which can store files larger than 4 GB, all of the video camera companies out in the market still split the video files into sections in order to work with the standard FAT32.
There is another reason why the video files are spliced as well, such as reserving system memory and preservation. Unfortunately, there is no way to force recording a long video into a single file unless it is a smart phone, which uses its own unique type of file system that overrides this limitation.