Possibly not, but my guess - and it is just that, a guess, so others on here may be able to enlighten us with the facts - is that the delay comes from two things; first the review of the portfolio and questioning of the Candidate by an Assessor, of which there are a limited number, and second, that the completed certification then needs to be signed off, as my guess (there's that word again) is that this is done remotely in batch, rather than on-site and on an individual basis.
The admin may be centralised, but I doubt all of the relevant staff are located in the same physical location, so it's probably not that they are all sitting in the same room (or even county) waiting for a completed portfolio to drop through the letter box.
Stuff gets sent around - remember it's a physical portfolio, not electronic - and because none of the staff are likely to be full-time salaried DMQ employees they have to fit this work in around their real jobs.