They have limited resources so they had to choose one. Same question could have been asked if they chose any of the others as well. Nothing prevents any other member of the UN from picking any other issue which they think is relevant and bringing it to the ICJ.

Gambia set the precedent with Myanmar a few years back.

Precedent was set back in the day by Liberia and Ethiopia when they approached the ICJ against South Africa’s apartheid regime in its mandate of (present day) Namibia in what came to be known as the South West Africa cases.

As regards the OP - it’s their call, it’s their prerogative.