Hi,
Look a this difference in appearance and Looks of the sewed thread and backstitching.
On the left: Smartphone Holster is made with #25 Needle and #270 bonded Nylon thread. Wathch the thick uggly layers when backstitched to lock the threads. Color Plays a role as well.
On the right: That Piece of leather is sewn with #23 needle an #138 bonded Nylon thread. Watch the allmost not noticeable backstitching (3 hole backstitch). It's way more beautifull than the thick thread.
So