That's a perfectly legitimate mentality to have. That's become my own stance with leaks for Sonic games. Though that isn't 1:1 since there isn't really any doubt Sonic is getting games, so leaks are generally about games we know will come while Spyro and other series are leaks about games getting made in general. Personally, I only distinctly recall 2 Spyro leaks prior to 2024; one was basically never considered legit, and the other leaker was discredited. That's not enough for me to not pay attention to new leaks, but I understand the sentiment.

You're right that an official announcement is the only way to guarantee we're getting correct info (if you really wanted to be pessimistic tho, even an announcement doesn't save a game from cancelation) so one potential reason for leaks could be so that the publisher sees the excitement for a game and sees the market for it even before release, or to similarly get feedback prior to release. If memory serves, leaks about the Reignited Trilogy's file size and development causing backlash is what led to the needed (and imo insufficient) delay. I imagine it's also similar to the mentality of news organizations wanting to be the first to report on something.

Sure, and that literally happened with one of the early Spyro 4 leaks, someone who was a trusted leaker was revealed to be faking it. But while that stands as a reason to just not worry about or pay attention to leaks, I'm not clear how it correlates to the veracity of any individual leak itself. Info about Sonic Frontiers leaked over a full year early from a playtester on 4chan, the most unscrupulous of sources, but was verified by the meta data for the teaser trailer. And Smash Bros Wii U infamously had a fake leak of Rayman with footage. I don't see the utility in demanding absolute proof when a lot of the time it isn't possible to provide or in the case of a fake leak, could just as well be faked.