A plateau feels like a market limit. Usually it is a structural one — something in the account that was fine at small scale and became the constraint.
1. You are buying the same demand harder
Extra budget goes into campaigns already saturating their audience. Impression share is high, CPCs climb, nothing new arrives. The fix is new coverage — search terms with no campaign, or a channel that creates demand rather than harvesting it.
2. Brand is masking flat performance
Brand traffic grows with your other marketing and lands in the ad reports. Blended numbers look stable while non-brand quietly stalls. Split it out and the picture usually changes.
3. The catalogue is the ceiling
A small number of products carry the account, and they are already maxed. Everything else has never been served or has never sold. Until the feed and the catalogue open up, more budget just bids harder on the same winners.
4. The offer stopped keeping up
Competitors improved their pricing, shipping or bundles and yours stayed still. Conversion rate slips, CPA rises, and it reads as an ads problem in the report. It is not.
Compare non-brand revenue this quarter against last, alongside impression share and conversion rate. Those three together tell you which of the four you are in, usually within an hour.