why wouldn't the pilot of '1DA speak up?

The simple answer is that you are not trained to "speak up" at a towered airport, you are trained to follow instructions from the tower and there is an assumption the tower will provide separation and appropriate clearances. As an ultimate fall back you are always supposed to "see and avoid".

For the official report you should reference the NTSB report but if you listen to the ATC audio in the linked video as well as their explanation of the link the pilots had no reason to think there was an issue and the clearances given were rushed but explicit. As I note above AOPA also notes

"it is a pilots responsibility to visually confirm final approach"

You can also hear that the pilot of '4SR was giving confusing instructions about base extension and clearance to land. The pilots was not incorrect in his approach actions but made a critical go-around error and may have been a low altitude, dirty config, stall.

Ultimately the lower aircraft on approach had the right of way so '1DA had no reason to speak up as they were in the right. AOPA states that the pilots may have thought "he was overtaking the aircraft from above" which is incorrect, or at least procedurally incorrect as '4SR would have had to yield to '1DA anyway.

In the end the controller should have simply issued

'4SR Go Around

Any time, you as a pilot hear that you should build the habit to just go around. As PIC you can ALWAYS execute a go around, controllers should be prepared for it and more importantly you as the PIC should be prepared for it.

It's the controller's responsibility to issue instructions and a pilot's responsibility to follow them unless doing so is unsafe. The pilot of 1DA didn't speak up because there was no reason to at that point; he didn't know of 4SR's intentions and probably thought that 4SR was going to fly a normal pattern just like the controller did. When he saw that 4SR was cutting the corner (obviously in a hurry, never a good thing) in front of him the instructor pilot of 1DA took control from the student and started a go around.

Going around is a busy time, you have to change pitch and power while maintaining airspeed and keeping the airplane in balance. The rule is Aviate, Navigate, Communicate, you don't make any radio communications until you have an established and controlled climb. 1DA would have made a going around call once that was done, but in any case the controller was, as the NTSB report says, "yelling" at 4SR so he wouldn't have been able to report anyway. 1DA wouldn't have reported number 1 because it's up to ATC to say who's #1, #2, etc.

4SR had multiple risk factors. According to the NTSB report it was 22 pounds under the weight limit (which incidentally meant it would have been over the limit on departure), and probably loaded with a C of G at or behind the rear limit. The pilot had elected to do a "slam dunk", close in approach rather than the normal pattern (probably intending to land long so there was less of a roll-out), was at a high approach speed and likely in a rush, with get-there-itis. The high weight would have increased stall speed and a rearward center of gravity would have decreased stability and control authority. The pilot jammed full throttle on quickly when at the limits of performance and couldn't maintain control.

Il était raisonnable pour 1DA de supposer que 4SR piloterait un modèle standard, mais Tower ne pas dire explicitement à 4SR qu'ils étaient n ° 2 et / ou confirmer qu'ils avaient du trafic en vue m'aurait rendu assez nerveux pour dire quelque chose. C'est peut-être parce que mon aéroport d'origine est très fréquenté et que la tour fait toujours les deux: elle ne vous autorisera pas à atterrir jusqu'à ce que vous signaliez tout le trafic précédent en vue OU qu'elle appelle votre base le étendu sous le vent (la norme) lorsque vous passez face à l'avion devant vous en finale. Ce genre d'accident est exactement pourquoi ils le font même si les règles VFR ne l'exigent pas.