not a single one uses your item = not viable
On the contrary, most of League of Legends players are young and not educated well, which means they are inexperienced in calculating in gaming, thus meaning their builds are plain dull and normal. Normal (meta) builds are no good. Denying this means you're an average LoL player (By intelligence, I don't give a rat's ass about divisions).
Example, one of the least bought items. Runaan's hurricane.
http://leagueoflegends.wikia.com/wiki/Runaan's_Hurricane
Check the link, and see how it stacks with certain champion's abilities.
Ashe's Frost Shot can now permanently slow 3 party members. So you become an ADC with a huge amount of CC, and that's a beast.
Caitlyn's auto attacks generate passive. With runaan's hurricane, it's more than 3 times as fast. If attacking from bush, every single auto attack should proc headshot (Not tested though, just a theory). If any meta guy would say that 50% bonus damage on each auto attack is useless, please, step aside, it's op.
Every 2. twisted fate's auto attack will proc his passive E with this item. Get 2.0 attack speed, and volia! You're doing 155 + 40%AP per second to single target (Tested it, worked perfectly). Again, can't call this useless.
Graves' cooldown on Quickdraw is reduced by 3 seconds per auto. With maxed attack speed and cdr, you should be able to use the spell approximately every 1 < x < 2 seconds. Combine it with Frozen mallet for perma slow 3 targets, Triforce to proc the spellblade so often, and with that (Silly) build, you can kite anyone forever, while still doing damage, + being tanky. Bruiser Graves op.
But wait, there's more.
Since runaan's hurricane procs on hit effects, other items benefit from it as well (Statikk Shiv procs insanely fast, 30 per hit, Frozen Mallet applies slow to all 3, etc.).
This is just a random example how a single item, one that's really rarely bought, can actually make your champion a whole lot stronger, to conclude:
Nobody buys your item means there's a small chance that you're a genious and other are idiots.