Why was Warrington Wolves v Wigan Warriors not a sell-out?

From Facebook page, Warrington Wolves-Warrington Guardian:

Simon Bishop: Lots of great performances but Roberts was outstanding. Hopefully more fans starting to understand what he brings to the team. He’s not a Sandow type, much more steady and subtle.

Alan Lawrinson: That was a brilliant game from start to finish. Defence was spot on and attack was just as good well done the hole team.

Al Worrall: Outstanding defence. Ratch was excellent and outclassed Tomkins. Roberts had fun and shone. Clark ran his blood to water. Forwards were immense. Only picky criticism is to tidy up and work on attack. More of the same please Wire.

Steve Bolger: Magnificent performance from the lads, great all round performance. To nil Wigan with the side they had was wonderful to watch.

Stuart Read: Was good to see Charnley sticking to his prematch promise and not “over” celebrating his try

By email to mparsons@guardiangrp.co.uk:

Ron Schofield: For a so called rugby league town (which it is!) I find it hard to comprehend that it wasn’t a sell out. The quarter final of the Challenge Cup and there were large spaces in the Warrington section. What do these supporters want? Great weather, a team playing very well and a derby game. Why don’t the people of Warrington turn out for such matches?

Probably because it was live on domestic TV..... reduce ticket prices & free tickets to schools.

— Phil G MCFC. (@PhilGreengbg) June 3, 2018

I'm sure whatever excuse people have they'll get around it for Wembley if they get there.  Then they'll sing Wire Till I Die despite it being their first game of the season.

— Sid (@sidneymufc) June 3, 2018

Why when was the last Warrington home sell out .probably had 1 in the last 15 years so its a ridiculous question to ask

— michael williamson (@michaelw0360) June 3, 2018

Does it really matter ? If people want to go to a game , any game, then that’s their choice. Over the last few years crowds for all clubs in the cup have seen poor attendances.

— Steve Clarke (@SteveCl56489969) June 4, 2018

Not seen the St's vs Hull attendance yet but I'm pretty sure all the Wire games in the rounds so far have had the greatest attendances.

— Andy Bibby (@AndrewPaulBibby) June 4, 2018

On Twitter:

Ryan Atkins: One of my favourite quarter finals that. The performance, the fans and the result. Congrats to my boy @Joshuacharnley on his 200th career try too. What a match to score it in.

Joe Philbin: Absolutely buzzing with that awesome performance from the boys. Big thanks to the fans atmosphere was electric, on to the semis we go

Richard Mathers: WHAT.A.PERFORMANCE. Man Of Steel/England levels by @Darylclark9

Max Holland: First class effort from @wolvesrl 1-17, but in particular, defensive efforts of @kevjonbrown and @Darylclark9 were outstanding. Hit everything that moved all day. Trojans.

Steve Price: “The zero against Wigan’s name is outstanding. That’s what we pride ourselves on here, being really sound defensively and working hard for each other. The guys typified our DNA.”