There are two other possibilities going on with this case.
1) After Blurred Lines case, these plaintiffs feel like having a go at the wheel of fortune too.
2) After a study of several years, the US Copyright office released a report in which it recommended some sweeping changes to US copyright laws to reflect how music is written, produced and distributed today –that might have an effect on suits like this.
In other words, they may be trying to get this suit filed while they still have the opportunity.