The primary reason is that I have had persistent audio issues with Steam Recording. It seems as if there is some additional noise suppression applied to the microphone, even if all of the Steam voice settings are configured to provide raw input only. It often clips the beginning of what I'm saying if I speak softly, and sometimes even when I am not speaking softly it still just intermittently fails to record me speaking.

The mic sounds fine in game and in other recording software, the culprit truly seems to be some inbuilt noise suppression within Steam Recording itself that can not be disabled. If anybody has fixed this PLEASE let me know.

This would not be nearly as much of an issue for me if we had the option to record the microphone audio to a separate audio track (like Shadowplay does), but since the buggy mic audio is permanently attached to the clip it basically 'taints' any recording in which the issue occurs, rendering it unfit for use. Even without the issue present it is nice to be able to selectively mute my mic audio afterwards for clips if I was making noise or my keyboard was too loud or whatever.

The other issue that I have had with Steam recording is the inability to review clips that are stored on a Hard Drive. The clips play back fine when viewing the created files after export but it will say "Recording Unavailable" or something along those lines when trying to view it within Steam.

This can be "solved" by recording to my SSD but the repeated writes and wipes are probably not good for my SSD, and obviously space there is a premium so I hate having to constantly clean clips out when I have a perfectly good 8tb HDD that Shadowplay has absolutely no issues recording to even at very high bitrates.

It's really a shame because otherwise the Steam Recording interface is miles ahead, and I love being able to clip what I want out of a background recording mid game. These issues make it really hard to use for a more "professional" setting over something like OBS or Shadowplay though (trying to actually publish your gameplay footage, not that I'm super professional or anything but you get what I mean, more serious users).