Because this is how evidence based reasoning works. If the evidence that is supposed to support the hypothesis is fundamentally flawed, then our hypothesis doesn't actually have any support.

The fact that we can apparently so easily find flaws in what is supposed to be empirical evidence should make us more cautious about drawing firm conclusions. In fact, low quality literature is something of a plague in many social sciences at the moment (e.g. the replication crisis in social psychology).

This post presents a decent discussion of this sort of issue https://www.cremieux.xyz/p/beware-the-man-of-many-studies