More meta than mechanical - as I stated above, divisions and limits are needed otherwise Zanz would be theorectically forced to implement a ridiculously large amount of pillars ingame.
For mechanical (again somewhat meta) justifications:
- Almost all of these elements interact with each other or have innate synergy in some way. Lava Golem, Steam Machine, Shockwave, Trident, Puffer Fish, Unstable Gas, etc... are some examples.
- 3 out of the 4 elements have a healing mechanic - the one that doesn't focuses on slowly picking off the opponent. When done right this can lead to some powerful stalls. Again, good combinations are common among these elements, though unlike the Material Elements they show through 2 card combinations (Crusader + Weapon, Thorn Carapace + Boneyard/Soul Catcher, Deathstalker + Eclipse).
- Similar to Spiritual elements has a lot of innate synergy between elements, though combos here are often more direct and/or become the focus of an entire deck or are a useful but somewhat situational niche (Fractal GotP/Charger for good midrange power, BH/Discord, Older FG farmers that relied on Anubis, Momentum + Quintessence, Supernova + RT/Lightning/Momentum, etc...)