Houston housing market

Obviously fully aware of the market trends right now. A solid 20-30k over asking price in houses selling within weeks of listing. My question is, where are folks getting SO MUCH cash to pay differences in lender appraisals? I suppose plenty of folks have savings but, covering down payment, closing costs and massive differences like that. I don't get it. One theory is a sudden influx of California residents coming in with alot more cash to work with, is this true? Also, why aren't sellers just listing their homes for what they are actually looking to get out of it? If we know the market says anywhere from 15-30k over, why not just list for that much? Guess I'm also slightly venting because of my growing frustration with my particular price range giving me hope and then being severely let down when the agents finally responding to my offers with "seller went with much higher offer"…. What's everyone's thoughts? Theories? Data?

Also, why don't sellers agents disclose what houses ended up selling for? I've only wanted to know how "bad" I was beat out so I can further understand where I stand/adjust my offer accordingly on the next one, etc.