Graduate students have like four good years of research time. If your work is scooped it will almost guarantee low citation counts but very likely it means that the work cannot be published at all. A year down the drain.

If you want a faculty position after graduation you've got one shot to create a strong research profile. Getting scooped once can close career doors forever.

People also often don't understand what grad students do. They do all of the research. 100% of it. PIs are funding the lab and providing mentorship. The first authors on major groundbreaking papers are usually grad students.