On your cheat sheet, you mistakenly have armor pen marks instead of magic pen marks.

Yeah you're probably right but I'm not the person that relies on his team to buy items like that. Usually in gold and lower the support buys randuins instead of frozen heart, but I'll edit some hp items in.

I'm aware of its stats being good but mostly being good on champions it suits. If you are playing against Irelia and an AD Carry your support is the first one opting to build this item or your top laner/ jungler (depends on champion). You as a carry are supposed to deal damage while surviving and therefore they "carry-saving" items are more valuable. Building health (Rylai's) is one of the common ways to survive Irelia.

Frozen heart is actually really good for the amount of armor and mana it gives, and it is really strong against irelia (a pick that is in 30% of the ranked games).

You should take a further look at your skill sequence because you missed out skilling your ultimate for the third time at level 16.
Frozen Heart is never really an option as an item because you're supposed to fullfil the role of an AP Carry (therefore just "carry-saving" defensive items like the other ones you're mentioning).