When the goal is to protect the lives of healthy cats, this method is clearly not ideal. Unfortunately, this is the most commonly used method nationwide. Over a period of 30 years, using the catch & kill method, there has been no significant decrease in the number of feral cats. The remaining cats in the colony aren't sterilized and continue to reproduce.
It is possible to decrease their numbers by adopting out the few feral cats who can be socialized and transitioned to live indoors. This is generally practiced along with Trap Neuter Release, but most feral cats can't thrive living indoors. They've lived their entire lives with very little to no human contact and are strongly bonded to the other cats in the colony.
Another common, but ineffective practice is trapping and relocating the colony. It may work temporarily and cause unnecessary stress on the cats, but it's likely that other cats will move into the area as the original colony is relocated.
For the cats that cannot be socialized, it may be possible to contain them in an enclosed barn, cattery or another structure to keep them safe from wildlife. This method can also cause unneccessary stress on the cats who aren't suited to living indoors. This is only a solution for a small number of cats, as there just aren't enough sanctuaries or places to properly house a large number of feral cats.