The original paper and referencing article are paywalled so I'm not sure if this is mentioned there, but the answer to the question "why did they use XXX for arrow points?" is surely answered by putting yourself in the position of "them" and thinking about how you'd get material for your arrows. No Amazon, no Home Depot. You'd wander around in your environment looking for suitable material. There are many places around where I live where the regular rock is soft (sandstone) but there are deposits of quartz here and there (no idea why, but there is a whole federal park devoted to the phenomenon[1]). So if you lived in such an area you'd use quartz because it's the only available usable material.

Only once long distance trade routes/gathering expeditions were a thing, people used material from further away. E.g. there are examples of obsidian from a specific location in Yellowstone being found up to a thousand miles away[2].

[1] https://www.fs.usda.gov/r01/beaverhead-deerlodge/recreation/...

[2] https://www.nps.gov/yell/learn/historyculture/obsidiancliff....