Because we don't have 5 sections that we can do every week right now or anything so it clearly will be sooo overwhelming compared to what we're used to.
They're doing it to:
1) limit faction for LFR people
2) limit faction for normal mode raiders who can't beat the content
3) string out LFR players subs
4) make it so a small number of normal raiders who can beat it fairly quickly can "see" it in normal before LFR
They could care less if people run 1 or 5 or 10 sections of LFR per week as long as they do it enough for them to continue justifying raid development costs.