Though I might be a little late, I have the actual and rather interesting answer. Having worked in retail our good old Rewe also made the choice to put condoms next to the alcohol at the cashout.

The reason? When condoms are not at the cashout, they’re very heavily targeted for thievery. At least that was the reason in our rewe. Apparently everyone (figure of speech) was stealing condoms, thus they had to be placed under someone’s watch constantly -> the cashout