Are you asking why SL inworld is so laggy?
I guess the reasons are bad scripts, sculpts, large textures but most of all the inconsiderate people who use/wear these heavy, high prim, high detail, scripted attachments. Think of it, most hair are made out of so many sculpts linked together and that's only for one av. If that's not bad enough, the scripted color change script, resize or other scripts in the attachments makes the lag even worse. If you go to a sims where there lots of sculpts to make buildings, it's always much laggier. Then there are unnecessarily high resolution textures being used for small object which makes loading textures longer.