This has been answered for you about 5 times on the official discord already today. I’ll copy and paste what Kain, an EHG dev, responded to you with on one of those attempts to answer your question:
"The game’s balance drastically changes with the number of skills you have at your disposal, the importance of each skill is reduced for each additional skill you can have at the same time, and there’s fewer decisions being made regarding your skills since the answer is just “everything”, and there’s fewer variations between different builds since they would all just run anything remotely applicable reducing the feeling of making “your” character.
By limiting to five skills, we aim to make each skill more individually interesting, and more meaningful when you interact with it. Instead of having a massive roster of individual skills, instead our skills offer skill trees which can completely change how the skill works, or even give it interactions with other skills, such as triggers which can allow builds to reach past the 5 skill limit to some extent.
The five skill limit is not a technical limitation, but one of intentional design within the game. While some of the examples are a bit outdated, we did a dev post regarding this and the design concepts still apply : Skills to Pay the Bills "
I hope, whether you agree with it or not, this sufficiently answers the question for you as to why EHG has chosen to go with 5 buttons.