“The indefatigable spirit of exploration” isn’t the answer. People, as a mass, only explore to find new resources due to scarcity.
There are exceptions, but they tend to be thrill seekers or publicity hounds seeking to capitalize on a measure of fame upon their return and dying on a spacecraft 1/5th of the way through its journey isn’t thrilling and no ticker tape parades await your return.
If you can build a spacecraft capable of sustaining 1,000 human lives for multiple centuries, you’ve solved all local resource scarcity problems. You could just mine the solar system and build billions of habitats that lazily circle the sun.
Hell, you wouldn’t even care about habitable planets anymore and a likely endpoint for any interstellar efforts would likely be a long-lived star with large orbiting gas giants you could turn into solid materials in order to build trillions of habitats orbiting that star, not an insignificant earth-like boulder.
Imagine turning all of the methane in a gas giant into carbon strands, using its hydrogen to do it and building a near-infinite number of habitats, each perfectly suited to human existence.
An earth-like planet with its quakes and tsunamis and seasonal cycles would seem pathetic.