What is wrong then, with Shell just buying on market, and only...

What is wrong then, with Shell just buying on market, and only tell/release an announcement whe they will reach the 14.99%, or whenever required by the regulators.

No one will know, and the sp will go up as required through the normal supply and demand.
After all the announcement of "Change in substantial holdings" does not need to be lodge fortwith as the buying goes on. By the time the announcement is due to be released, and has been released to the market, too late, the bird has flown.

Buddy