[tyingq]

He had presumably used it for 10 years successfully. Surely he gained some expertise over that time period.

[paxys]

He probably just got a new competitor in the space. Easy to see good returns on online ad spend when all traffic just goes to you by default.

[theptip]

Ad noob here; how would you test this hypothesis?

[grugagag]

Or returns gradually went down until it stopped working altogether.