Like all employees of the FBI, James Comey lives off the sweat of the American taxpayer. His large salary, upon retirement, will be converted into a very generous pension. Like most federal employees in a high ranking position like his, Comey continues to look forward to decades of living at a standard of living far above what is experienced by ordinary people in the private sector.
To maintain this life of comfort, all he had to do was agree to look the other way as a powerful politician clearly — by Comey's own admission — broke federal law.
Naturally, this same treatment would never be afforded to an ordinary taxpayer, who would likely be looking at years in federal prison for offenses similar to that which Hillary Clinton has apparently committed. Moreover, Comey even went out of his way to do his best to ensure no federal prosecutor would proceed with charges when he claimed that "no reasonable prosecutor" would proceed with charges. It wasn't enough for Comey to simply not recommend charges. He had to pre-emptively condemn any prosecutor who might proceed with charges.
Some have claimed that Comey was forced to cave to Obama administration pressure in order to protect his family. Of course, Comey could have resigned his position rather than take a position he regarded as unethical. Then the task of clearing Clinton would have fallen to Comey's successor. There are precedents for this. When ordered by Nixon to fire the special prosecutor in the Watergate scandal, Attorney General Elliot Richardson resigned rather than do what the president mandated. Comey could have done the same, but then he would have had to give up some of his comforts and privileges. To find work, he might have had to move to an unexciting place like Indianapolis or Albuquerque.