I believe he was referring to the total number of people worldwide who keep kosher.
In areas with any significant population of those keeping kosher, food manufacturers generally decide it's worth the expense to follow the laws of kashrut and to have the line supervised. This also happens with major manufacturers, whose foods are distributed on a wide basis and to a broad demograophic.
In areas where there's a relatively small population keeping kosher, it becomes either a matter of economics or the owner's personal preference/belief.

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> Hi Alex,
>
> Where did you get your figure of 5 million worldwide? Is this for milk
> allergy or all food allergies?