There are reasons.......
There are two main issues with Femto.
From the Network Operators view, they can interfere with the MacroCell network. RBS's have a bell curve coverage map [with the RBS in the middle - peak- of the bell curve], and the network planning and dimensioning takes this into effect and maps and overlaps RBS's to give a uniform coverage.
Femto, being 'closed' to the household, often with no more then 4 or eight users, interferes with this bell curve and can actually reduce RBS's coverage. It also means there is no 'public' handover from an RBS to a Macro, which in turn can lead to a dropped call. This is supposed to be managed by the Radio Access Controller, but as this may not be connected directly to the correct MSC, [unless the MSC's are in 'pool'] then this too gives the NOC added complexity.
The other issue with Femto is also their advantage. That the fixed line operator carries the bulk of the 'in building' coverage, which means the fixed line operator has to be connected to the RAC. If it is not, because the user takes their home package from another supplier, Femto's won't work.
Femtos /can/ be used in an SME or Corporate location, to provide in building coverage, but this is usually mapped into the NOC coverage plan, and frankly there are not enough SME's nor Corporates who need to add in building coverage, hence the low take up of Femto's.
From a consumer point of view, why do you need the extra hardware in the home if you already have a fixed line broadband connection ? You can use wifi on most devices these days to connect to the internet and carry voip traffic, such as skype and sip. Are there really that many consumers that do not have in home coverage to receive the occasional call ? It seems not, again, the reason for the low take up of Femto's.
Small cells will never really replace RBS's, for most of these reasons.
It /will/ be intersting to see how the 'small cells' progress, but I suspect they will not set the world alight.........