The attacks are believed to be in retaliation to revelations of America's own hacking attempts on Iran, specifically the use of the Stuxnet virus in the nation's nuclear infrastructure. While the DDoS attacks against US banks and the NYSE did little more than knock those services offline for a few hours, the attack on the dam in Rye marked a worrying shift in their tactics. Though they were unsuccessful in taking over the dam's controls, this was the first time that the Iranians had attacked a piece of physical infrastructure in the US.
The men -- Ahmad Fathi, Hamid Firoozi, Amin Shokohi, Omid Ghaffarinia, Nader Saedi, Sadegh Ahmadzadegan and Sina Keissar -- all work for Iranian cybersecurity companies and live in Iran. As such, there isn't much chance that they'll actually be tried. It is, as the NY Times points out, more of a symbolic gesture to Iran, a "we see what you did there" move, much like when the DoJ indicted a cadre of Chinese hackers working for the PLA back in 2014.