>>106244419
because you downloaded one without embedded subtitles. idk why some of them do that
you can embed them yourself if you like, for example;
ffmpeg -i s01e01.mp4 -i english.srt -i spanish.srt -c copy s01e01.mkv
or if you prefer a gui, you can try mkvtoolnix-gui, where you can drag in the video and subtitle files and mux them into a new file. either method is as quick as your drive can make a copy, and doesn't affect video/audio quality as it's not transcoding anything