There's risk and reward for the Bears trying to pull off the double trade down.
Risk: The Bears trade with Houston, Carolina waits to determine if they trade, or how much they are willing to trade, until they know who Houston takes at #1. This possibly affects their willingness to trade Moore, how much draft capital they will give up, or if they are willing to trade up with the Bears at all. Maybe even shifting their focus to Arizona as a trade target as well.
Reward: The Bears gain the extra pick/picks from Houston, but presumably also get less from Carolina to move to #2 instead of to #1, even if everything else remains the same. So the reward on trying to double trade down is the difference of what's gained from Houston vs. what's lost with Carolina.
Even if we go with your position that Moore is a fringe top 20 WR, there doesn't appear that there was a better path to obtaining a WR1 this offseason, and it was important to be able to make that happen now for Fields and his timeline. The possibility of losing out on Moore alone is enough for me to forego the potential reward of waiting, or trying to pull off a double trade down. The outlook with Moore/Claypool/Mooney is completely different than with Claypool/Mooney/WR3.