Fusion is heart/enotions that is why the Superpoly Ritual needed the emotions of multiple people
Synchro is mind/focus this is why you need a CLEAR MIND to truly master it
XYZ is body/evolution that is why there is a focus on change through rank-ups
Links are cold logic that is why only artifical intelligence was able to create the top level ones
Pendulums are harmony between two distinct things, that is why they need another pendulum to work and why they can be both monster and spell
Rituals are dedication, through either prayer (why a lot of ritual support is angel/holy themed) or occult methods you have repeated something often enough to master it