So the article kind of lays out why the IG report was delayed.
In May, the President delegated (not abdicated, as the article states), broad declassification authority to the AG. The President has also directed Departments and Agency to provide (pretty much anything and everything) to the AG.
So a lot of stuff that had been held back was made available, and takes time to review. If things come to light, they too must be investigated.
Also, reports have been published that some people who had previously refused to be interviewed, have recently agreed (perhaps not a coincidence). Also reportedly, at least one person has recently agreed to cooperate.
So the job is just not done, until those threads have been followed.
When it is done, there is a period of a few weeks, when folks who are implicated in wrongdoing are allowed to review the parts relevant to them, and submit their comments, before the draft is finalized. Then there are a few weeks where the final draft is briefed and reviewed up the chain of command, before going public. (I assume that review to identify classified or otherwise restricted (e.g. Grand Jury, ongoing investigation) information will have been done ahead of time - if not, that would be another delay).
It has happened before, that late breaking info delayed the IG report. It looks like that has happened this time too.
Each new little straw delays release of the whole thing.
So a lot of stuff that had been held back was made available, and takes time to review.
Only if there is no sense of urgency and they are working bankers hours. Mueller had perjury traps, indictments and guilty pleas in months. Horowitz isn’t even running a criminal investigation. He should be able to move even faster than Mueller did.
Where there is a will, there is a way. Meuller had a strong desire to assault POTUS and his supporters. Horowitz does not have an equally strong desire to preserve the rule of law and pursue criminal Democrats to the benefit of POTUS. Sorry.
Any possible crimes found by the IG are supposed to be sent to the DOJ immediately as criminal referrals. They are not supposed to wait for a report to be released.
So where are all those criminal referrals from the IG?
It's not a good sign when the IG has had 16 months to investigate without sending any criminal referrals.
So the article kind of lays out why the IG report was delayed.