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.
In my perspective only long-term holders are having big role in building new ATHs; buyers and sellers are having their own reasons to do so but whenever there will be less number of sell orders then we will have huge rally which will end up in setting up new ATH. So, the role of long-term holders must be vital. If we need to thank shorters are providing liquidity then we must treat in the same way for longers as well.