There could be several explanations for what we see on that graph, maybe developers are just being cautious and prefer to wait for the merge to happen before deploying their smart contract, or maybe they cannot wait for the merge to happen and decided to change the platform where they were going to release their smart contract, and finally this could be simply the effects of the bear market we are going through and it is affecting not only the price of ethereum but the amount of smart contracts as well.
I do believe that simple affects of bear market would be the smartest answer to this. I believe that it is mostly about that and nothing more. I am not saying that there isn't a situation where we can't see ethereum going up again, there will be a situation where bull market will come back and we will see ethereum doing amazingly and that sounds like a very possible situation.
Of course, not everyone thinks that this will be the situation, some believe ETH is gone because of the proof of stake situation coming and miners leaving. But I do not believe that, as long as projects still start their projects on ETH, it will continue to survive and be big.