Daryl has mentioned in the past that they should be doing that.
That would be far too much common sense for this series, which features characters making irrational decisions every step of the way, as though they have learned nothing from surviving in a world overrun with zombies.
The producers continue to have the characters act this way for the sake of false drama. Some characters are interesting, but they end up suffering when the main plots must have most making assbrained mistakes or motivated by decisions anyone would see as a disaster in the making.
The other thing is, even if the decomposition process is slowed, these zombies are obviously rotting away-- how many months or years will it be before the zombie herds become completely unjustifiable?
The producer argument against that is "new zombies are created all the time," so when the older ghouls decompose beyond functionality, there's another generation to replace them.