I guess it's legal and most likely what's happening.
From the point of view of a high-profile investor, however, keeping information, such as the investor's identity, secret while accumulating shares of a public company can offer that investor a significant financial (and legal) advantage.
Well, it's a good way to accumulate a large stake of shares while under the radar and avoiding SEC regulations
Good way to buy up 100M shares and turn that into billions.
High-profile investors don't like the public at large knowing what stocks they're investing in. Multi-millionaire investors don't want a bunch of little fish buying the same stocks that they have targeted for large volume share purchases - the little guys run up the prices.