It is just that you have not done before. If someone threw you a basketball and you had never dribbled it you would suck but nothing wrong with the ball or you just need practice. Most do not get rough enough with them or use thin plastic to allow it to slide.
I went to our local technical college and took a course in auto upholstery. The instructor took and interior out, took the seat covers apart, door panels off, cut patterns and sewed the covers and panels and installed in a 4 hour class. NOT ME, lol. It does get easier, go to the net and watch videos and it helps to have someone else to hold things also. Good hog ring pliers are a must. Lost mine have to find new ones.
Some new padding and maybe burlap is usually need to get everything to fit nice. Also if springs are rusty take the time to get them back to looking great.
Steam and sunlight always makes them look better.
I actually bought my own Singer commercial upholstery sewing machine. They fly sew about 11" a second if you floor it which you never do, lol. They were cheap when all the textile plants closed in the south $300 and will sew through a half inch of material easily. Can sew nylon straps or anything.
David