why can i rotate screen and have sound at the same time. Why is only option one or the other

Do you really think it's not possible to do both and set them up the way that you want them to be set up? You just don't understand how the process works.

System sounds can be muted and controlled two different ways. The screen lock rotation can be controlled in the same manner as well.

Settings>General>Use Side Switch to: Mute System sounds. If this option is selected, the switch on the side of the iPad above the volume rocker will mute system sounds.

If you choose Lock Screen Rotation, then the switch locks the screen. If the screen is locked, you will see a lock icon in the upper right corner next to the battery indicator gauge.

If you have the side switch set to lock screen rotation then the system sound control is in the control center if you are running iOS 7. Swipe up from the bottom of the screen to get to control center . Tap on the bell icon and system sounds will return.

If you have the side switch set to mute system sounds, then the screen lock can be accessed in the same manner as described above.

This support article from Apple explains how the side switch works.

http://support.apple.com/kb/HT4085

You can have both, it simply controls which one is controlled by side switch, set it for mute and then slide it off, now you have sound and rotation, slide it on, and you have muted sound but not affected rotation, set it for rotation slide it off and you have both, slide it on and you have locked rotation but have sound, also whichever one it is not set for is then available for control in the control center (slide up bottom center of home screen)

Make sure both the side switch and the mute/ lock rotation icon in Control Center are turned off.