Kafka is well documented and understood. Your custom postgres solution is not.
Best case you write high quality maintainable code and have a single dependency. Worst case is you create a complete mess that takes months to onboard people.
Right now I'm contracting on a project that uses AWS BATCH, docker, kubernetes, terraform, Nextflow, Django and postgres. It took me 2 days to on-board myself and start delivering features because everything was standard.