What is SRT?
SubRip subtitles are about as simple as a file format gets: a number, a start and end time, the lines of text, a blank line, repeat. Nearly every video player and editor on earth reads them.
What is ASS?
ASS (Advanced SubStation Alpha) is the subtitle format for people who care where the text sits: styles, positioning, fonts, karaoke timing. Anime fansubs made it standard. Converting it to a plain format means the words survive and the choreography does not.