Leaving your ex to initiate all contacts is giving up any control you have over the situation. Your ex gets to decide the when, how and what, and all you can do is wait or react.
It’s a place of powerlessness and can cause a lot of anxiety and fear especially when your ex takes too long to initiate contact. You’re left anxious and fearful that you might never hear from them again.
Sadly, there is always the possibility that you might never hear from your ex again.
Even an ex who is initially interested may decide that you are not interested and/or being the only trying to keep the lines of communication open is not worth it.