This comes up on pretty much every missing person thread and the answer I think is both simple and complicated.
Everyone's lives and ways of interacting are different and whilst it's easy to use hindsight it would be extremely unusal for anyone'e first thought on not hearing from someone to be that they'd be kidnapped/murdered etc. You'd think phone problems, overslept, forgot first IMO, you don't ring the police because you think you're overreacting, you'd be embarrassed to be wrong, maybe they had a fight on the phone there could be many reasons. Of course you try friends and family first and over a course of time you exhaust all the mundane options before raising a formal alarm
JMO
And you don't have to wait for 24 hours btw, just in case you are ever in that situation