The reasons why cats get ear mites if they don’t go out:

1. Cats carry ear mites themselves. Cats themselves can also carry parasites, but the symptoms are not obvious at first, and they will become more and more serious over time.

2. Family members have been exposed to sources of infection. If someone has had contact with a cat or dog infected with ear mites outside and petted their own cat without disinfecting it in time, they are likely to be infected indirectly.

3. There are other pets in the home that carry parasites. Ear mites are highly contagious and can be passed across species.

4. The cat’s living environment is not clean. Cats living in places that are too dark, humid, and dirty for a long time are likely to breed bacteria and mites.

5. Failure to clean the cat’s ears regularly. If your cat's ears are not cleaned for too long, oil will accumulate in the ear canal, providing a good breeding space for mites.

6. Water gets into the cat’s ears when bathing the cat. After water enters the cat's ears, it will not dry naturally, but it will also cause the cat's ears to become inflamed.