Amazon is a business, not a process. You have to adapt based on your results.

The scaling process it not easy. The PPC process it not easy.

To scale a product you have to lower the best seller rank by a lot...dramatically...and know that your product will have enough organic sales strength to sustain the new found sales velocity somewhat while you reduce ads so you can make a profit to make up for what you lost.

A lot of times the play is to break even in about 4 months but, at that point, you have a listing with a ton of sales history, reviews, and sales velocity so its just a matter of restocking.

PPC is incredibly annoying. In no way shape or form is it set it and forget it. I have keyword action days (3 per week) where I negate/add/improve keywords. And every monday i reset my bidding strategy to account for any changes in impression behavior (like losing a ton of impressions to other sellers who are increasing their bids the night of thanksgiving so I am no longer winning any placements anymore).

I can see that your SKU has not had any dramatic improvements in best seller rank in the 150 day history it has. I would say that its because your PPC process is not good enough.