Because the soil wick in them only pulls up water to the roots as needed and it keeps the soil moisture levels consistent rather than soaking wet-dry-wet-dry. They also encourage deeper root development while top watering only encourages shallow root development.

The roots never get drenched, compacted, and O2 deprived as they do with top watering.

Unfortunately, too many mistakenly think that "maintain consistent soil moisture levels" means watering at the same time every day.

Dave

IF you have the right soil mix. as long as it wicks water but not sponge. also has aeration, using something like perlite. the right mix is the key.