For me, it is simply the fact I am a complete noob. I spent six hours putting together 40 rounds, my first 40 ever.
I figured it was the cheapest round I could practice on, with the least potential of hurting me if I really messed up.
I think the only thing I didn't do twice was seat primers! I hope to get out Wed and see how I did.
I'll be glad to start on larger cases, my fingers can barely be made to work those tiny components. I'm getting into it primarily for the .300wm and .45/70. I've collected a decent amount of brass for those, and they are spendy as all get out for good loads.