To answer all your points individually:
How come Slaking learns only Status and Physical moves ?
It doesn't, it learns a ton of Special moves by TM and move tutor. But no special moves by level up. Slaking is a physical Pokemon (160 Attack vs 95 Special Attack) so physical moves are much better suited.
If Slaking is so lazy to move why does it learn Physical moves ? Special attacks would fit more because it is so lazy.
Like NO1974 said, who says special moves are easier? Slaking is a big powerful Pokemon so just lashing out is easier than doing something special.
It is tired to move so why doesn't it learn any Special attacks ? Wouldn't it be better if it attacked by distance ?
That still requires effort. And perhaps more effort to attack from a distance. Slaking has Truant so it only attacks half the time, because it's lazy.
Please don't answer with Game Freak Wanted That Way.
Well, that is the real answer, so...