This galaxy is frippin' BIG. Even with practical FTL, it could take a long time for an intelligent species to spread through the galaxy
Time is also big.
If it takes 1000 years on average to colonise and develop a new planetary system to the point where it's willing and able to spin off its own colonies, and each successful colony produces just one child colony every thousand years (allowing for failed colonies, colonies that don't further colonisation, etc), it would take just 38 thousand years to colonise all 200 billion stars in this galaxy.
Even allowing for a practical limit of 1% of the speed of light, if it is even possible to reach another star system, you can colonise the entire galaxy in just a few million years.
If just one civilisation in the last few billion years had a culture of colonisation even a fraction as much as humans do, the entire galaxy would have been colonised, even without FTL. And colonised repeatedly, in thousands of waves, exploiting every niche. We simply wouldn't have had a chance to exist.
and it's plausible that such an advanced civilization wouldn't really be interested in what happened on planets.
All of them?
Not a single faction from a single alien civilisation is interested in other early intelligences? We study dolphins and chimps. We study parrots and ravens. Hell, there are researchers who study ants, lichen, plankton...