According to combat designer Noel Chamberlain who is working on Suicide Squad Kill The Justice League, there is a soft cap on the skills you can earn during the game’s story. However, you can earn more skills during the end-game content.
“You cannot unlock all the skills. You can obtain skill points every time you level up, but that alone will stop at a soft cap. You can get more skill points from end-game content after clearing the story, but it’s not enough to unlock all the skills.”
So what’s the solution? Developers are making up for this by allowing players to freely respec at any point, with 0 cost. This means you can customize your build freely even if you can’t unlock all skills.