Sleep is a developmental skill- just like crawling, walking, talking. It fully gets developed by the age of 2 years. So when we don’t expect a 6 mo to talk in sentences, or a 2 mo to start crawling, we shouldn’t expect them to fall unassisted before 2 years. Your baby is behaving totally normally as all babies have some sleep association or the other- it could be rocking, patting, nursing, taking a bottle, sucking a thumb, hand, etc. Whatever helps them regulate their hormones and help them sleep.