Using armor or shield without profiency

[Loorti]

Why my wanna-be melee sorcerer (half-orc with str 16) can't use armors and shields? I could easily use leather all day long with minimal spell failure chance.

'Nonproficient with Armor Worn: A character who wears armor and/or uses a shield with which he is not proficient takes the armor’s (and/or shield’s) armor check penalty on attack rolls as well as on all Dex– and Str-based ability and skill checks. The penalty for non-proficiency with armor stacks with the penalty for shields.'

Source: http://www.d20pfsrd.com/equipment-/armor#TOC-Armor-Check-Penalty