I have no idea why, and the free form of the system is extremely flexible... .
There is a strange skewing in Words of Power vs. regular magic. In regular magic the wizard is supreme in flexibility because they potentially can cast any spell, they just have to prepare it. Words of Power doesn't change that. In fact, because the list of Words of Power is so limited compared to the MASS of regular spells available, you could say a Word wizard is less flexible, (maybe better to say less potential).
Because a spontaneous caster can build spells on the fly, a Words sorcerer is probably a better choice. Maybe even better than a regular sorcerer, at least again as far as flexibility.
That's the weird thing. Words of Power sorcerer = good, Words of Power wizard = meh.
Also, while Words of power have a few tweaks, like the 1st level Fade-Conceal which when Boosted is like a 1 round improved invisibility or the Fortify-Body spell that is +1 to saves and gives temporary hit points, sometimes they are weaker than regular spells. Sometimes because the target words make them trickier to use, like having to hit with a ranged touch attack to heal.
Also, one thing I really didn't like when I read Words of Power is that each caster is essentially limited by the type of spell they could cast regularly. Clerics heal and wizards blast things. Meh.
As that one podcast said, I see awesome roleplaying potential with words of power. My summoner took the Experimental Spellcaster feat and my idea behind learning about words of power was through his eidolon, which is a manifestation of a forgotten primordial power, so words of power seemed like a good mesh.