Because you should never just 'trust' random 'research'. Good analysis in this case will clearly explain the problem, the analysis methodology, findings, net effects, resolution, etc. Something you can read, and decide for yourself whether it is complete/incomplete, has holes, contradictions, etc. Not 'we looked into it and all is good - only potentially tiny effect' (no actual data or methodology presented at all) and then linking to a comment directly contradicting the claim...

It's a hilariously unserious and untrustworthy response.

It's not that people are entitled. It's that "do your own research" is usually a cop out when you yourself don't understand the answer or are hiding it

Arguably the initial post was meant to convey confidence and authority on the subject. When questioned you could either dive deeper and explain in more detail why x because of y (if so inclined), ignore it, or... do what they did.

No one owes anyone anything, but if you want to represent something; answering the question more in detail would have either closed the issue or raised more scrutiny, both of which are a good thing when trying to figure something out.

I don't have to trust someone to check their research and look at how they worked. If the work doesn't pass muster, likely the results don't either. Again, you can view it as entitlement, but if you're not going to bother backing up your claim, why make the claim to start with?

That's silly. If they show their work I won't have to trust them. Compare answering "The answer is 5, just compute it yourself." on a math test, vs. actually showing the calculation. The former clearly implies the person doesn't know what they're talking about.