Ai, ai captain!
Thx for catching this I wanted to post it but well my screen shot is lost in the terabytes...
My theory of why the depth looks like it does:
Sellers know they'll get their price so aren't taking big dumps. Buyers know this so there is no incentive for smart/large buyer to put up a bid and of course doing so is counterproductive in that it shows the sellers that the interest is there. This could cause sellers to pull back.
So you get this chart with a sharp knife of bids and a low bump of asks.
A few sell walls do exist. It is uncertain whether these are legitimate or attempts at manipulation. The manipulation could be to hold the price down but it could be to try to suck buyers up and then reform the wall at a higher price.
So the buyers slowly creep the price up without creating much fervor and then CHOMP! Eat a huge chunk out of the ask wall.
It the movie "Tremors" but in chart form
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W 
