Do you think after they develop a new miner they mine on altcoin first for months before they release it and then after they sold those miners they gradually sold their coins gradually?
I dont think that is true.
miner manufacturers must back test their product, to know the stability, the hash rates, room temperature etc before it can be successfully sold since every buyers are interested in knowing such information before placing an order, certain coin earned through such mining shall be sold.
This is the main reason why the price of bitcoin and altcoin drop a lot and I think those who produce the ASIC miner are those who selling big amount of BTC and altcoin.
Btc have 21M total supply, we can all watch the remaining btc on the blockchain, i do not believe that is the reason for price drop.