Volume is calculated from daily buy and sell trades. Maybe there is just more of day traders that are buying crypto and selling it in some hours after they get a necessary profit? In such case you can take your 100$ and buy BTC and then sell it untill exchange fee won't eat all money. In this case those 100$ will cause thousands of trade volume.
all traders are only looking for profit, nothing else. so after buying and already feeling enough to profit, they will sell it. This is a common thing. So investors will come back if they feel crypto is giving them profits and that is now happening with many new investors entering crypto.