The Root Causes of Steady Weekly Decline
Steady weekly decline is almost always caused by one of three things: stale content (players run out of things to do), broken retention hooks (the systems that used to bring players back have stopped working), or community decay (your Discord or social presence is dying).
Identify which of the three applies to you by looking at your analytics. If session length is dropping, it's content. If D1 is stable but D7 is dropping, it's retention hooks. If community metrics are dropping, it's community decay.
For developers still at the concept stage, the BLOXG AI game maker is the step before any of this: a written description in, a publishable game out, under your own Roblox account.