Another reason might be that several years ago RD was removed from the SP500. Institutions holding shares of all the SP500 stocks as an indexed portfolio no longer need to hold RD. CVX and XOM are both in the SP500.
A Significant reason is that RDS is a foreign company and many of the institutions invest in only US companies and/or invest in stock indices which hold only US stocks. And, those institutions which invest in foreign stocks invest world-wide and thus normally would hold only a small % of RDS.