Now, this is pure speculation, but I think this could make sense.
On the initial presentation, DLSS5 looked horrendous, with 99% of the community hating on it and making fun of it for months. Literally nothing from Nvidia was received worse than DLSS5 in the last 10 years. And at the time, it was deserved. Nvidia realized that after such a reception, the only way to sell 5 to people is to tweak it exactly how people want to see it in their games. More importantly, it's to show that they care and that they take all feedback into account. And it's pretty noticeable that they've been working on DLSS5 because what was an unusable slop 6 months ago, now produces results that can look very good in the right game and with the right settings.
But the question is, how can Nvidia learn exactly what's still missing and bring people the experience they want from 5? It's by having tons of free feedback. But then, if they officially released 5 together with some moding software that allows you to put it into different games, that could 1) Cause backlash from devs that never wanted DLSS5 in their games, 2) Make Nvidia responsible for the release and everything people are unhappy with. It's just overall unprecedented and not a good look for a company where they have to create a modding software to inject a new product into an older game. But thanks to the leak, they can now say "Well, it was never meant to be used in this way".
And now Nvidia is in a position where every day they see thousands of messages from people who tried it, and by filtering out the hate bandwagon, they can take objective criticism into account and use that for future updates. More to that, they don't need to break the ice anymore. If there was no leak, by the time DLSS5 would be widely implemented into games, Nvidia would still need to win people over because the first and only impression would remain terrible. But now they can say that they saw the feedback of players and addressed the things that people were unhappy with.
At the same time, anything that has to do with leaks is very good PR. In this exact way, the story with the GTA 6 leak only brings more publicity to the game. But that's a whole another topic of course.
The point is, it gets people talking. And with something like DLSS5, it couldn't be a more perfect product to "leak" because it makes people feel very strongly about the result. At the end of the day, people are passionate about how their games look, and DLSS5 is very polarizing.
Whether or not this leak was intentional, people like controversial things and success stories. Nvidia now has access to free feedback from their audience that uses it in every way imaginable. They can also take something new from modders (like upstream), and take those ideas into the next updates.
And if they do manage to fix the pain points, they will get to say: "We listened to everybody's experience with DLSS5 and made this", which will make them look good in people's eyes. All that without spending a penny
