(Bloomberg) In recent years, founders of big tech companies have realized that they can take their companies public while still maintaining control in perpetuity, by setting up dual- or even triple-class stock structures and issuing low- or even nonvoting stock to the public. A lot of people have worried about this, but now they can stop worrying: That trend is over. I mean, Facebook Inc. and Alphabet Inc. and Snap Inc. have already done it, but don’t expect too many more, because S&P Dow Jones Indices has announced that the S&P 500 and some of its other big indexes “will no longer add companies with multiple share class structures.” Existing multiple-class companies (like Alphabet and Facebook — but not Snap, which never made it into the S&P 500) will stay.