Why that items?
Because a say so, that's why...

Nha, is because urgot have a really low range in his basic attacks so he docent need attack speed or crit, he need to build damage and mana because he is a mana junky champion in the early game.
his main damage comes from the combo of E and Q, you lock the target and u hit it from a large distance

soo to explain why the items:

Why Muramana: you need mana, mana regen and damage you get that from it

Why Bloodthirster: you need the damage and the life steel for sustain in the lain

Why ionian boots: you need the CD your main damage are the spells

Why the black cleaver: damage, CD , life and armor penetration, plus the passive works when you use E

Why frozen heart: it gives mana so it gives you attack damage because of muramana, CD ,and armor so your not that squishy

Why runaans hurricane it make 2 other targets get your passive so it helps a lot in team fights