what s the reason of this big decrease?
I think the reason is pretty obvious. There is no "decrease", just returning to the same levels that BTX was before the weekly airdrops started. Not just the price is returning, but also the volume.
All that talk "against" the BTX rich people ("split-cheater", really ?), and modification of rules in favor of those that only want "free" coins but don't want to buy a single BTX with their cash, is making the pricing drop. For those that can read between lines it's clear that some "riches" stopped buying BTX (perhaps also started selling some), and with fewer people buying and miners selling, the price drops.
This behaviour can be easily viewed checking the BTX market graphs, that show us a BIG increase in BTX volume and price when the weekly airdrop rules motivated the "riches" to buy and compete against them. It seems to me that most of the BTX "riches" are silent buyers and don't want to write posts or entering discussions here, but at the end, those "riches" were making every BTX holder also richer.
We can discuss about what is fair o not, ethical or unethical, but those are the facts that the market is showing us (if we want to understand them). It's up to us (the BTX community and devs) to decide the fate of the coin, but I see here a bit of the old axiom capitalism-comunism.
I don't undertand why so many posts against the BTX riches (envy ?) because as far as I understand, those that are rich are because they paid for the BTX and risk their money doing that. It's almost impossible to be a BTX rich only linking BTC because even if you have 100 BTC (almost $300,000 - a nice amount), that only gives you 100 BTX which is about $170 at today prices. So, there are no free BTX "riches"; the riches are those that are risking their capital supporting this coin. All my respect and thanks to them.
My opinion is that we need to motivate the people to buy the coin, and if the "whales" and "riches" can and want to do it, that will be in benefit of all BTX holders. Not to mention that higher market capitalization and higher volumes also benefits the coin to get listed in bigger exchanges.