It's a core balance/game design issue for DnD that's been this way since Basic.
Up until very recently, one of the core concepts of DnD is that you have a small team of highly specialized PCs each solving problems in their own area. You have the spell guy, the heal guy, the tank/bruiser and so on, everyone has their own thing.
Strength and Intelligence are the two 'power attributes' that everyone gets use out of but are primary to fighters/barbarians/etc and wizards/arcane spellcasters respectively. As such, a Str/Int race is ideal for both diametrically opposed classes as well as Gish builds. Both class types are very powerful in Pathfinder, combining the two has to be handled delicately to maintain game balance especially when you consider PFS legality.
Touch attacks, for example, exist to give low-strength, low-BAB spellcasters a chance to actually do something hand to hand, give them higher strength or the ability to optimize for str and int you're going to get synergies that the devs probably don't want to deal with.
This isn't to say that it can't be done in a balanced way, I'm sure it can, but it's a worry and that probably makes it a low priority for the devs. As such even if you get an official str/int race (or more if one already exists, I can't think of one off the top of my head) don't expect them not to have some downside.
Edit: To be clear, I love the Magus and other fighting casters and yes, those classes would benefit from Str/int races. Of course, I mostly build Dex/int style characters when I go for this archetype so I haven't noticed the lack of Str/Int but I wouldn't turn back a player in a home game that brought me a concept for such a race built with APG.