Aphids are known to be attracted towards tomato plants much more so than other plants. However, another factor to consider is because aphids are also particularly attracted to plants with new soft growth of fruits. There could also be some activities that you may be indulging in that could be leading to the continued return of aphids, such as over-watering your tomato plants or even over-fertilizing them. It is best to use preventative measures, such as the use of traps or companion plants to prevent this from further happening.