The Cochrane review did not ask the question of whether Lecanemab (for example) worked, it asked the more general question of whether targeting amyloid worked. If targeting amyloid, generally, worked you might expect all approaches to targeting amyloid to show some efficacy. So they included all those for which clinical trials had been conducted. Obviously some treatments didn't pass the threshold required and so were not subsequently approved. If you only included successful trials you would bias the outcome.

It's possible, of course, that some methods of targeting amyloid might work where others failed. But even those that claim success (Donanemab and Lecanemab) have a very modest benefit.