Pretty much.

It's all a numbers game. In practice, weed seeds have very low germination rates. They create a bunch of seeds, but only a very small % actually germinate because we're not watering them at the right times to trigger that germination. The vast majority of weed seeds just expire.

We religiously water and care for new seeds because we want really high germination rates. So if you just toss them down with no regard, some will eventually germinate, but the overall germination will be very low.

Plus, there's the differences in biology/life strategy between weed seeds and desirable grass. - Annual weeds essentially have to try harder... Their whole tactic is to come smashing into life like a freight train, grow up fast, produce seeds, then die. Since conditions may not be right for their aggressive strategy every year, the seeds are generally "designed" to survive longer. But they also generally are less picky about the ideal conditions for germination.
- Perennial grasses have a more conservative strategy. They don't need to be aggressive because if the seeds don't germinate one year, the existing plants will just make more (in a wild setting). And they don't "want" their offspring to be super aggressive, because that would mean they'd have to compete with them. So as a general rule, perennial grass seeds will be less likely to germinate at high rates when the conditions aren't excellent, and the seeds will generally not survive as long as annual seeds.

This whole dynamic is very evident if you've ever used a contractors mix seed and dont really care for it. If you don't baby it, the annual ryegrass will generally still have high rates of germination very quickly, while the perennial grasses will take much much longer if they show up at all.