I haven't heard that phrase specifically before but it is likely to mean that the person can't gain interest in the topic. For example, if there's a movie you don't like, you would say, "I couldn't really get into it." If there is something you don't want to talk about, you would say, "I don't want to get into it." Hope this proves helpful.

Usually people say, I can't really get into it= I'm not very interested I don't get it= I don't understand

Usually "I'm not into it" or "I can't really get into it" or "That's not my thing"

it means i'm not interested or im not involved.