Despite the progression in technology, a close, cropped lawn is threatened by thatch, which is a matted layer of dead grass clippings that accumulates at the soil line.
Thatch blocks water and air from getting into the ground and builds on itself.
Enter the mulching mower, a rotary mower on which the blades keep the clippings airborne for a while, flailing them around and chopping them up before dropping them back on the ground. The small pieces decompose quickly enough to avoid the problem of thatch buildup.
However, you can avoid thatch buildup with a conventional mower by cutting frequently or collecting the clippings.
But that's either extra work or depriving your lawn of the clippings, which are beneficial. Decomposing clippings become food for earthworms and other organisms that aerate the soil. Eventually the clippings turn to humus, which helps nourish the lawn and soaks up moisture between rains or waterings.
Either buy a mulching blade to fit your rotary mower, or go out and buy a bonafide mulching mower.