I think the biggest reason that forces players to nuke all stat points into one is the diminishing stat scores per level. At first my mage was splitting points between AGI and WIS, only to realize that I was only maintaining power, not increasing. Each level up, all my score %s drop, and it requires all 10 stats to gain back the diminished loss. As it stands, my 300 wisdom mage only gets ~28% to apply ailments, which has not changed since level one. His spell casting speed was at +10% from agility around level 2-3, it's now dropped to 2% without a pure agility investment.

I love how spread the important scores are, but enforcing diminishing scores on level up seems counter intuitive to build diversity when we are forced to nuke all our points into one stat just to maintain the core of our build.