Cats defecating indiscriminately in the house can be caused by a variety of reasons. Here are some common possibilities:
1. Stress: Cats may experience stress due to changes in their environment, changes in family members, or the addition of a new pet. This stress can lead to anxiety and, in turn, inappropriate defecation.
2. Heat cycle: Unneutered cats may mark their territory with urine during their heat cycle, which is a common reason why cats defecate indiscriminately.

3. Litter box issues: If the litter box is in an unsuitable location, too dirty, or has an odor, or if the quality of the litter does not suit the cat's preferences, the cat may refuse to use the litter box and choose to defecate elsewhere instead.
4. Health problems: Certain health conditions, such as urinary tract infections, kidney problems, or diabetes, can also cause cats to defecate inappropriately.