"If they could get it, why didn't the CRA and other tax authorities know? How come the tax authorities couldn't get it?"

Silly question with the following possible answers: 1) They just didn't tell the CRA; 2) They carefully structured their affairs so they told the CRA what was legally required, but were able to avoid revealing important details (a more sophisticated and legal version of answer (1).  They hire very smart lawyers and accountants for this purpose); 3) The CRA knew but didn't care because the legal forms were followed.  That is why whoever has access is releasing this to journalists.  Journalists are performing their role in the democratic political system of shining a light in dark corners and making bureaucrats accountable and the rich squirm.  Much of this tax activity may be legal (slavery was once legal) but the public will be concerned not with narrow legality but with the ethics and morality of what has been revealed.