Lets say it like this (without knowing the tool, the authors, and with all due respect):
The tool was published in 2014 as an online application. That means there must be a server backend somewhere that requires maintenance and creates costs. Funding is and has always been limited in the academic world. Often software gets abandoned at some point, either after the first authors leaves the lab, or when funding drops out, or simply because at some point people have different focuses and projects to work on and nobody has time left to provide proper maintenance of the code base or (in this case) hardware. Any of this could be the reason, it is not clear whether the tool still exists and whether it comes back online. You can of course contact the corresponding author, or you can try to use any other tool. Hope that helps at least a bit.