Thanks to them, but thanks to the buyers also. Without them, those sell orders wouldn't have been filled.
Indeed. Not only those who sell their Bitcoin, but the buyers also have a big role. Both of them have a big contribution to support the Bitcoin ATH. I also one of them who sell Bitcoin, but only a few of all the Bitcoin I have. So, just thanks to me, guys! 
The long-term holders have a big contribution as well. If all long-term holders sell their Bitcoin, I think the rice of Bitcoin probably suddenly drops in the market because of the increase of the supply. Well, all the parties basically contribute to support the Bitcoin ATH.