Somehow they noticed you and they came to see you. There may be something there.
In order to acquire them, you need to get them signed up (or you need to make a connection). This is a critical step that has to be made. You cannot market to them effectively if you do not have a connection to them, which they have willingly accepted. They will forget you.
Every buyer faces an ongoing individual battle with how to allocate their attention. There are numerous responsibilities, problems, needs, and wants, that are competing for that attention. If they came to see you, there is something that may be of value to them. But if you do not have a way to stay in touch, while they go through their process of addressing their needs, you will fade away amongst all the noise.
Every buyer goes about deciding on new products or services in their own way, and at their own pace. It could be haphazard. It could be structured. In order to nurture an ongoing relationship, you need to acquire their contact info.
Developing an acquisition model is about finding ways to provide them some value here and now, in exchange for their sign up.