Here's why:

* Sporophytes are diploid: They have two sets of chromosomes, one from each parent.

* Spores are haploid: They have only one set of chromosomes.

* Meiosis is a cell division process that reduces the chromosome number by half: This is necessary to produce haploid spores from a diploid sporophyte.

In contrast, mitosis produces genetically identical daughter cells with the same number of chromosomes as the parent cell.