how come the "generalist tank build" always cycles back
with boots and another item whether that be sustain, dmg, or cancer 
remember tank fizz? frozen fist poopy? reworked yorick first month? now its Galio zzzz
with boots and another item whether that be sustain, dmg, or cancer 
remember tank fizz? frozen fist poopy? reworked yorick first month? now its Galio zzzz
Tanks don't really have much options? lol What do you expect them to build?
because armor penetration is op and pure resistance builds are in most cases trash.
if a tank wants to be relevant, he needs to build some amount of damage, as its more efficient to deal damage back to the carry and dispose of him quickly than trying to build more defenses and tank him.
especially as someone who has kog maw i his name, this should be clear what i mean. there is not much point in building to tank someone like a lategame kog maw. killing him with your team by contributing some damage is often just the more efficient route.
Just to add onto this. Pure defensive items like FH and Randuin's provide more than tankiness, they provide debuffs. It's much easier to do well as a tank when you have tank items that do more than just allow you to take more hits.