What would drive it upwards is the lack of selling and not buying and that is something people have been missing out for a long time honestly
No, it doesn't work that way
The lack of selling coupled with the lack of buying (cause otherwise we would see prices rising steadily) means less liquidity in the market. And the latter inevitably leads to higher volatility, not the consistent upward momentum
Why would there be less sellers? Because every other way of making a profit is actually lacking and everything goes down, whereas bitcoin is a great long term investment for you, hence people would not sell their coins to keep making profit instead, and as long as we go up like we do right now there is no reason to keep selling so they will keep it instead (or "hodl" for better understanding)
Things are obviously a lot more complicated than that
As I'm inclined to think, most of the price action that we saw recently is explained by squeezes, both long and short ones. So it doesn't matter whether "Bitcoin is a great long term investment" or not (while we are at it, this mantra doesn't seem to work anymore either). Sellers can sell on margin, just as buyers can buy on margin too, and this is what has been going on for quite some time now. Put differently, sellers, or lack thereof, as you mean them and as we know them, don't play a significant role in this game of stakes