The reason is actually to protect you (I know, seems counterintuitive). If your company did not have a policy of refusing tips, the IRS would assume you get them and tax you on them whether you got them or not (they do this to table servers). Because it is far more common to not tip at a concession stand than to tip. Most businesses where tips aren't standard, have a policy to reject tips (even if it's not enforced).
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