1984 was when the GRO went all computerised, so the data was already available, so low cost. They could have done the same with births and marriages if it was not for their rule about being too close to the present.
They also changed to monthly reporting rather than quarterly. FreeBMD doesn't show that in the search results; you have to click the "spectacles" link to see the month of registration, so it is struggling to fit it in the existing structure.
Sorry but this is not correct, the GRO is not yet “ all computerised” but has the following digital records available:-
Births: 1837 – 1934 and 2007 on
Deaths: 1837 – 1957 and 2007 on
Marriages: 2011 on
Civil Partnerships: 2005 on”
The DoVE (Digitisation of Vital Events) project, which provided the early records noted above was not initiated until 2005 and the contract expired at the end of July 2008.
Cheers
Guy