Is this you? If so, why aren't you seeking out more work to do, since you have so much free time?
I know this sounds snarky, but I have never seen a company that didn't have undone work. And I've rarely met colleagues who didn't appreciate a helping hand when they were busy.
It comes down to cost-benefit: on net, will doing this thing create more positive things (e.g., personal reward, recognition, compensation) than negative things (e.g., dealing with bureaucracy, being hassled, getting entangled in organizational politics)? If it's net negative, there's no reason to do it. Now, that's inherently pessimistic, but that doesn't mean that it doesn't apply to actual work environments. There's also an argument for recognizing this situation and doing something about it (i.e. quitting to do something else), although that can be easier said than done, depending on one's circumstances.
Likely: zero equity, and a negotiated wage that is less than the opportunity-cost of one's time because it had an expectation of "slack" calculated into it by the employer. Most retail jobs have these properties.
I worked and managed retail for several years. There was always more work that needed to be done. Retail stores are messy, and sales correlate positively with clean, attractive merchandising. Customers are needy, and sales correlate positively with customer service.
I didn't mean "slack" as in "free time because there isn't anything to do"; I meant "slack" as in "extra tolerance because—at a given wage—an average employee will predictably goof off X% of the time."
This is how all large chains (McDonalds, WalMart, etc.) are managed from a corporate perspective. Instead of paying X salary to ensure enough "morale" for optimal worker productivity, it is actually more cost-effective to pay workers a lower wage such that they're sub-optimally productive—but still productive—and then put systems in place to both idiot-proof and peer-quality-check each employee's output, such that the output is still guaranteed even with multiple "malfunctioning" process-nodes potentially touching it.
The epitome of this approach is seen in how an "automatic" Amazon Mechanical Turk work pipeline operates at scale: a program hands off work-items to workers, and then treats each individual work-product as being of unknown quality, handing it off to further workers to give a quality-judgement to it, cross-checking those workers' opinions in case some of them are just mashing "good", etc. None of this would be necessary if the work paid well-enough for market-forces to apply (i.e. if people would want to compete for the work.) But since it doesn't pay, people aren't interested in one-upping one-another's quality to steal the job, so you just end up with whoever decided to wander in.
See also: the economic "Losers" in the MacLeod Hierarchy.
I know this sounds snarky, but I have never seen a company that didn't have undone work. And I've rarely met colleagues who didn't appreciate a helping hand when they were busy.