I do not believe Hall vs Valencia killed it. It was just another data point in a long-running downhill slide for the event. Below are the match-ups for the previous three years in reverse order, 2018, then 2017, then 2016. Some pretty good match-ups, but others (pre-season rankings), were 6 vs 18, 12 vs 13, 4 vs 9, 1 vs 6, and on and on. Many top wrestlers stayed away, dating back years.
141: Joey McKenna (Ohio State) Vs. Kaid Brock (Oklahoma State)
149: Mitch Finesilver (Duke) Vs Matt Kolodzik (Princeton)
174: Myles Amine (Michigan) Vs. Jacobe Smith (Oklahoma State)
184: Max Dean (Cornell) Vs. Taylor Venz (Nebraska)
285: Derek White (Oklahoma St.) Vs. Youssif Hemida (Maryland)
125: Nick Piccininni (Oklahoma State) VS Darian Cruz (Lehigh)
133: Seth Gross (South Dakota State) VS Stevan Micic (Michigan)
141: Kevin Jack (NC State) VS Bryce Meredith (Wyoming)
149: Max Thomsen (Northern Iowa) VS Matthew Kolodzik (Princeton)
157: B.J. Clagon (Rider) VS Alec Pantaleo (Michigan)
165: Chad Walsh (Rider) VS Jonathan Schleifer (Princeton)
174: Zahid Valencia (Arizona State) VS Mark Hall (Penn State)
184: Pete Renda (NC State) VS Drew Foster (Northern Iowa)
197: Michael Macchiavello (NC State) VS Frank Mattiace (Penn)
285: Nick Nevills (Penn State) VS Tanner Hall (Arizona State)
125: Barlow McGhee, Jr. (Missouri) vs. Nathan Kraisser, Sr. (Campbell)
133: Zane Richards, Sr. (Illinois) vs. Eric Montoya, Sr. (Nebraska)
141: Bryce Meredith, Jr. (Wyoming) vs. Anthony Ashnault, Jr. (Rutgers)
149: Lavion Mayes, Sr. (Missouri) vs. Anthony Collica, Sr. (Oklahoma State)
157: Brian Murphy, Sr. (Michigan) vs. Max Rohskopf, Sr. (NC State)
165: Isaac Jordan, Sr. (Wisconsin) vs. Daniel Lewis, So. (Missouri)
174: Ethan Ramos, Jr. (North Carolina) vs. Zac Brunson, Sr. (Illinois)
184: Gabe Dean, Sr. (Cornell) vs. Myles Martin, So. (Ohio State)
197: Brett Pfarr, Sr. (Minnesota) vs. Brett Harner, Sr. (Princeton)
285: Ty Walz, Sr. (Virginia Tech) vs. Connor Medbery, Sr. (Wisconsin)