If this is your reasoning what are you even doing here? Anyone can look at recent eBay sales and note prices.
Yes, there is a reason. Because when you post a book that sold people in this community are interested in whether that sale is an anomaly or part of a trend. Since people here make money, some their entire living, off the comics market this sort of thing matters.
Cable and Deadpool 50 is being bought and sold currently due to misinformation. It was previously bought and sold because its a final issue, until recently when some people made sure to mention it all over the comics-related internet as it being the first appearance of Venompool. Incorrectly. This results in eBay sellers incorrectly touting it as the first appearance of Venompool and buyers of varying intelligence purchasing it as a result. Where were these sellers advertising this book as the first appearance of Venompool a year ago? Two years ago? Venompool has been around for roughly 5 years so why the discnnect? This isn't a coincidence. Its almost like market manipulation is real.
Why does this matter, I mean who cares about the insufficiently_thoughtful_person buyers who don't know any better? Well if you're going to buy into a book it just kind of sort of matters if the interest in that book is genuine or built on lies. That maybe kind of sort of gives an indication of where the book will be valued next week, next month, next year. And call me crazy but some sellers might actually care if what they are selling is the real thing or a fugazi.
This. Makes. My. Head. Explode. (insert exploding head emoji here)