Probably just the way they are made. Why don't you just look into other brands (Anderson, Pella, etc.) and find ones you like?
Don't confuse poor quality vinyl products with their premium counterparts. My last home here in WI had 20+ yr old vinyl windows that still worked and sealed great, and that was with an outdated design and technology. I will say though that in hot climates (like Texas, AZ, etc), aluminum windows are a good choice. I'm not really sure about GA though.You may lose some slight efficiency w/ aluminum, but it pays to go aluminum in the long run ... much more durable, longer lasting, won't sag, crack ... or require such wide frames.
I bought vinyl recently to be more energy efficient, but now I've been reading how vinyl is not holding up long-term. Its just too much work replacing a window to have to do it again in a few years.
Me replacing old wooden windows w/ new vinyl windows.