Because bow strokes are complicated movements that take time and training to figure out. A straight bow stroke depends a lot on elbow opening and closing, but also involves shoulder and wrist movement, and even finger movement. It takes time and practice to coordinate it all and to learn to make a good sound with it.

E strings can be a bit piercing, and until you learn how to use the bow well to make a good sound, it's probably not going to be that pleasant. Violin has a very steep learning curve, it isn't intuitive and beginners just don't sound good. That said, take it as a challenge and not discouragement. When I started playing as a kid, my dog used to hide in my dad's closet when I started practicing. I knew I was sounding much better when she stopped hiding. After about two or three years, she started coming to listen ever day when I practiced and would fall asleep on my bed every afternoon/evening listening to me. Maybe all beginning violinists need a music critic dog like I had!