I think that this year and last year the DfT wanted to avoid negative publicity seen in previous years; to do this they have:
- pushed back the annual increase a couple of months to March
- prevented new fares being visible/sold until the date of the actual change
The idea is that journalists will have hopefully forgotten about the annual fare increase by March and that even if they do remember, they won't have time to do any research regarding the new fares, and therefore negative publicity will be avoided.
If anyone can provide an alternative explanation, I am all ears, but I am pretty sure the above likely covers it!