Why do pros not seem to like building last whisper items (mainly ADCs, but everyone is included)?

and are both armor pen items which offer 25%-35% armor pen respectively. But rarely do I see them purchased (in NA at least). Usually in terms of armor pen, it is either not used at all or only through and/or lethality items. Rarely do you ever see either of the Last Whisper items. Rarely do you even see , usually if the lane match-up is heavy sustain like Vlad or something, but even then it ins't always taken. IDK if it is a pro thing, or if they can't work it into their preferred build's alternatives. But it would seem useful for games with a lot of AD heavy damage on your team where enemy champions can stack armor, or the enemy team has a lot of healing.

As an example, in today's match of TSM vs FLY, TSM had 3 heavy AD champions. FLY had an Ornn who build almost entirely armor, and a Yuumi. Yet only Dardoch and Broken Blade built . Dardoch did get a last whisper technically, but the game was already over when he did get it (it was already pointless to get it because there was no possible way TSM could contest FLY at that point with Elder buff and Bjerg dead with 0 nexus towers). But no armor pen on arguably the champion who would need it the most, the ADC. 4 of 5 members of FLY had at least 1 armor item. I get Aphelios has some armor pen built in, but it is that really enough? Also, only Pantheon had heal reduction too, vs a Yuumi who spam heals, an MF with a BF, and a Lee Sin who has built in healing. Not to mention FLY had a Mountain Soul. Is it just not a possible item for ADC players to build in PRO games?