1) Not enough photons reach the sensor to distinguish the object you are trying to photograph from the noise floor of the sensor. This is by far the biggest reason to go for a tracking mount.
2) You bog your computer down in post processing. 50x1 minute images are far simpler to align than 500x6 seconds images.
Combine (1) and (2), and there's barely any reason to go for untracked shots. As for satellites, planes, clouds, or other kind of transient phenomena that can potentially ruin a shot, that's where you apply some kind of clipping over data (usually sigma clipping or some variation of it) and problem solved.
I love the age we're in where anybody with a little know how can cheaply/affordably build something that was only available to the very well funded before. Each one of these are attempting the same thing, but trying to avoid the pain points each dev has seen from other products.
https://i.imgur.com/QD32T7r.png
They show all the other trackers with an Alt-Az wedge, but show their tracker without that piece, to make the other trackers look big.
With the specific 2 other trackers pictured, you can detach that wedge and use them exactly like the MSM tracker without their Alt-Az mounts and they would be a lot smaller.
Personally I own a SkyGuider Pro and use it with a pan-tilt head tripod and no wedge.
Is it simply image quality? Or are there more trade offs?
Why do this? If you do single long exposure, there is a very good chance your image will have an airplane fly through, a satellite streak by, or something more terrestrial like a fellow stargazer shining a laser through your frame, car headlights, etc. Taking a series of short exposures limits those issues, and if it happens, you throw out that shot and only loose 45-60 seconds instead of 15 minutes.
Stacking can also use shots you take when the lens is covered called dark frames. You take this for the same exposure time as the normal shots. This provides a noise pattern that builds up in any electronic sensor as the heat builds up from staying energized for so long (as well as natural summertime heat). That noise pattern can then be subtracted by the stacking software. The stacking software can also realign the images so you can use shots from multiple shoot days (er, nights).