Cynical answer: Because at big tech companies culture leads them to believe they have to have a competing product in every new market rather than letting their "competitors" go unopposed. Occasionally it works out, but often you just get a ton of also-rans. The companies are so big a profitable that even complete failure barely moves the stock price.

Nobody is incentivized to point out the proverbial emperor has no clothes. Top execs have something they can point to as "innovation" for a few quarters. Lower leadership for the project has their kingdom expanded and probably comes out the other end better off career wise. I would imagine its most frustrating for the actual IC's and PM's who pour their lives into something that eventually just gets unceremoniously deprecated, but they get to cash some pretty good paychecks and it probably helps their careers as well.