Remux to MKV but add all streams using FFmpeg

I'm trying to automate FFmpeg to remux all video files in a given directory to MKV. I'm currently using

ffmpeg -i $INPUT -c copy $OUTPUT.mkv

However, some streams are skipped that way - for example, if there are 2 audio streams only 1 goes to the output file.

How do I specify that all streams from the input must be copied to the output?

Since I'm trying to automate FFmpeg, it would be best if the command does not change for each file, i.e. manually specifying all the streams with -map would require me to first parse every file. I would do this if I need to, but if there is a better solution I'd prefer that.