To maximize profits and costs they can go after, and to be a bit less on the radar of the public eye. Now that palworld is essentially done making money, Nintendo can go after that amount.

Say it is the throwing spheres that Nintendo is basing the suit off of. If Nintendo tried suing in the midst of its popularity, palworld could have just switched the capture system to like a special gun or cubes or something. Nintendo wanted to wait in order to financially crush them into dust.