I’ve always had troubles activating my core even on squats etcetera. I got very lean, and still didn’t have abs to show for it,
I imagine there are a lot of parameters at play. Your insides pushing out, the size of your abdominal muscles, and how the fascia is laid out over those muscles. I imagine stomach vacuums were in vogue for a reason, and I’ve heard something about how the transversus abdominis and linea alba having a relationship with one another.
And obviously, genetics impact fat distribution and insulin sensitivity so.