You will note that I wrote, "I think". So, let's check and see:
Season 2010/11
Cardiff City
home - Tue 14 Sep
away - Tue 22 Feb
Sheffield United
home - Wed 10 Nov
away - Tue 1 Feb
Season 2009/10
Crystal Palace
home - Tue 20 Oct
away - Tue 16 Mar
Bristol City
home - Tue 8 Dec
away - Tue 16 Feb
Doncaster Rovers
home - Tue 9 Feb
away - Tue 23 Feb
Season 2008/09
Walsall
home - Tue 21 Oct
away - Tue 3 Feb
Brighton
away - Tue 28 Oct
home - Tue 27 Jan
Yeovil
home - Tue 11 Nov
away - Mon 19 Jan (brought forward a day for TV)
OK, not every midweek game matches up home and away but I think there's enough of an indication there that "it started three years ago". I remember noting the phenomena at the time and the ptb obviously feel that there is reason to extend it.
In two of the seasons one of the Christmas games 'pairs' with one of the Easter games, which has also happens next season - spion notes these as the "Monday games" for this season.
When I started to go to football, clubs always played in pairs home and away over both the Christmas and the Easter periods. There was a period since then when pairs of clubs played each other home and away midweek very early in the season. Both of these things fell by the wayside.
If you go back to the period immediately after WW1, you will find that all clubs played each other home and away in successive games throughout the season for about five or six years.
There have been various patterns in the fixture planning over the years. Clearly home and away midweek returns are now in vogue.