Square reached too high a valuation off of low value business with merchants. They have burned through staggering amounts of cash, canceled high profiled products, and purchased payment-unrelated startups and made other changes. The high valuation they've had in funding rounds makes them an unattractive purchase because the business they have isn't worth what it would cost. To get new money they'd have to do something like foursquare did to raise money, which dilutes everyone's current equity to very little.
They probably can turn it into some kind of business but the growth has stalled, the equity employees have is at risk and they've all but lost the sparkle that excites the press when they talk about the company. They could gain momentum back, it's not impossible, and they have really, really good engineers and designers so that's a plus.