In the long run resource shortage goes down. Technology increases the amount of output possible for a given amount of effort over a given amount of matter. For example: wood to coal to oil to nuclear. Thinking about starships of 3000 AD we're talking about a thousand years of scientific development towards nuclear reactors, food processing, scientific computing, and random technologies I can't even fathom because they'll rest on a bed of mathematics and physics that's not even conceivable yet.

If more technologically advanced aliens exist then our not sensing them is much more likely because they don't want to be sensed than some other consideration like them stopping to setup on some habitable planet. I'm horrified about war, and I'd hope they would be too, but it may be that aliens come to understand species or ecosystems in a more expansive way and may consider the process of ending war as a necessary one for the maturation of an ecosystem.

Or the great filter is true. We all end up killing ourselves because it's impossible to escape exponential technology growth and mismatched incentive problems, or something else like that.

It's always going to be a small percentage that desires to venture further out to new areas. On a newly settled planet, most will not want to leave. But some will.

But you have to wait for that society to forget that living on a starship means spending your whole life never venturing out, while a planet lets you spend your life exploring.

Or, you know, some just want to get away from the other individuals.

That is, if we are talking about something comparable to current humans. Immortal super AIs might don't care about idling in the void for a few million years, just for the opportunity to re-sync those gained experiences to their decentralized knowledge a few million years down the line. I really like the single omnipotent AI scenario, since being immortal and not depending on others changes quite drastically what strategies can be successful - it won't be anything like human kings who need to keep their subjects at bay and working for them to support their power and limited life. But we shouldn't restrict our imagination, if we are talking about possibilities and galactic time-spans.

The important part is, as mentioned by GP, the desire to expand, since this is a dominant strategy. In comparison, not every living being on earth has the drive to participate in evolution by e.g. creating offspring. Those usually just drop out of the "game" and likely won't matter in the long term, at worst making it a bit harder for the others initially till their disappearance. What matters are those who have persistent impact... e.g. by colonizing/making offspring.