why does my apple watch8 8 go to sleep?

OK....one last place to check. Open the Settings App on your Apple Watch. Scan up till you see Battery. Is Low Power Mode turned on by chance? If it is, turn it off. If this isn't it, you'll need to reach out to Apple directly for help.

Let's also clarify what you mean when you say the watch goes to sleep. Is the screen going completely black with nothing on the screen? I ask, because even with Always On turned on an Apple Watch, the screen remains active for 15 or 70 seconds, whichever you've set it up to be. But the screen should not go completely black with Always On turned on.

On your watch screen, swipe up from the bottom of the screen to open Control Center. Look for the icon with two theater masks and if highlighted, tap it to turn off Theater Mode.

Are you referring to the Always On feature? If so, see the 'How to turn the Always On feature on or off' section in:

Use the Always On feature with your Apple Watch - Apple Support