Because accuracy is the most important stat in the game, as far as combat is concerned. It takes significantly more damage, often at least a 2:1 ratio, to be worth taking an accuracy penalty.
You see a similar phenomenon in video games (particularly MMOs) that include an accuracy stat. Accuracy is the most important stat, up until the moment when you hit 100% accuracy. At which point, literally anything further spent on accuracy is totally worthless, contributing nothing. Some games (such as FFXIV and WoW) eventually removed* accuracy/"hit rating" as stats, because they didn't contribute anything to the play experience (but tended to do weird/bad things to stuff like raid progression groups).
People have mentioned the crit-fishing benefit, but the simple accuracy benefit is also sizable. If you normally hit 60% of the time, with triple-advantage you hit over 93% of the time. If you would normally only hit 30% of the time, triple-advantage gives you more than a 65% chance to hit. IOW, Elven Accuracy can turn battles that should be "just run, you have no hope in hell" into "this is reasonably achievable," so long as you still have any chance at all of hitting in the first place. And, as noted, you can push yourself up to over 14% chance to crit, so not only are you hitting far more often, more of your hits will be crits, too.
Part of the benefit of Elven Accuracy is that 5e's designers ended up doing exactly what I predicted they'd do: they've handed out Advantage like candy. When Advantage is commonplace, Elven Accuracy is undeniably powerful. And there are plenty of ways to either finagle Advantage from your DM, or just create it via mechanics--there have to be, because of stuff like how Rogues depend on it to get their bonus damage. Can't have balance-critical benefits that simply fail to trigger most of the time. Advantage tried to serve as both the "big benefit you hand out for fun ideas" option, AND the "first-resort so we can keep things simple" option, and those two things don't mesh together in game design. Having them be one and the same means the thing is going to show up everywhere, yet be a big deal.
Elven Accuracy is one of the only things that improves on normal Advantage, it's available to every character of two of the most popular (and strongest) races in the game, it's stupidly under-priced as a half-feat (especially one that can apply to any one of 3 stats), and it as noted applies to accuracy, the most important thing to optimize for combat.
Using your comparison to Lucky, OP: Lucky gives you 3 rolls per day, no more and no less. It provides no stat bonuses and can't be used more than three times before a long rest. Elven Accuracy is on 24/7, so long as you have advantage--and it's quite easy to get advantage on more than three attack rolls in a given adventuring day, thus exceeding the benefit of Lucky and getting +1 Dex/Int/Cha as well. The one benefit Lucky has that Elven Accuracy does not is that Lucky is both offensive and defensive. But overall, EA is just a stronger feat.
*AIUI, WoW just baleeted Accuracy entirely. FFXIV replaced Accuracy with Direct Hit, which is sort of like a mini-crit, that can stack with an actual crit. Mathematically, this was equivalent to juggling the numbers, but the vital difference is that there is no "cutoff" value for DH; it continues to be useful no matter how much you get. Instead of creating un-fun perverse incentives, they actually encouraged analysis and nuance.