because small companies can't get away with paying poverty wages. amazon jobs are ubiquitous and well-known enough that people treat it as a fallback. if you can't find a better job, you go work in the amazon warehouse or as a wal-mart cashier, because they're always hiring.
companies that don't operate on the same scale aren't constantly hiring, so they can't get the same benefit of being the fallback option for people and have to offer wages that are high enough to actually attract employees.