Because they're on their way to world domination

Those of us who have been blessed to be owned by cats know that cats are the ones that genetically engineered us for our thumbs so we could open the bag of kibble, or even better, operate the can opener. Science hasn't come out in support of that, yet, but there is a report that

Cats 'exploit' humans by purring

Since each of these sounds is produced by a different mechanism, cats are able to embed a high-pitched cry in an otherwise relaxing purr.

'How urgent and unpleasant the purr is seems to depend on how much energy the cat puts into producing that cry,' said Dr McComb.

Previous studies have found similarities between a domestic cat's cry and the cry of a human baby - a sound that humans are highly sensitive to.

Dr McComb said that the cry occurs at a low level in cats' normal purring. 'But we think that (they) learn to dramatically exaggerate it when it proves effective in generating a response from humans.'

Yes, definitely on their way to dominating the planet....