In regards to WWE's announcement about the on-sale date for WrestleMania 37 tickets being pushed back, Dave Meltzer of Wrestling Observer is reporting that the decision to delay the sale was a last-minute one made on either Sunday or Monday. 

There is speculation that WWE is looking to increase the event to full-capacity from the 45,000 fans they originally planned.

UFC recently announced they have plans to have a PPV event in April with a full-capacity indoor crowd, WWE might be trying to run even bigger and looking into the logistics of doing so.

"We’ll have to see if Vince is gonna go for the full stadium. The plan was 45,000 seats, but that changed obviously because they didn’t put tickets on sale."

"They pulled the stuff earlier today [Monday], so it’s not like it was something that was decided even like Sunday. It was decided today, maybe Sunday, but they pulled the tickets today."