There is no real good answer for the title question. From Byron York at washingtonexaminer.com:
The memos are critically important. Portions of them have been leaked to the press, given to a Comey friend, discussed in congressional testimony, and read by a few Capitol Hill lawmakers and staff. Sometimes it seems the only people who have never had a chance to see the Comey memos are the millions of Americans who are trying to make sense of the daily firehose of Trump-Russia news.
They’re not likely to see the memos anytime soon. The FBI and the office of Trump-Russia special counsel Robert Mueller have imposed tight restrictions on access to the memos, holding them even more closely than some documents that are classified at a far higher level. Now, with speculation about obstruction ever present in the media, some lawmakers are calling for the memos to be released. It’s time for Americans to know what’s going on, they say.
The public part of the memo story began on May 16, 2017, when the New York Times published a story headlined, “Comey Memo Says Trump Asked Him to End Flynn Investigation.” The paper reported that a Comey-penned memo detailing a Trump-Comey conversation the day after the firing of national security adviser Michael Flynn was “part of a paper trail Mr. Comey created documenting what he perceived as the president’s improper efforts to influence a continuing investigation.”
“An FBI agent’s contemporaneous notes are widely held up in court as credible evidence of conversations,” the Times added.
To continue reading: Why are the Comey memos secret?