You can do research during your postdoc with chill timelines and pretty much 100% autonomy on your topic and then bootstrap a company with the ideas you've developed during said postdoc? In many countries the postdoc owns the IP of the research they're doing

i never heard of the postdoc owning the IP. it's always the university

Postdoc can be very advantageous on a resume. Where I am, if it's remotely related, you start at a higher engineering level than a PhD.

Big opportunity cost.

It's significantly easier to get a Visa from academia than work

Good point, didn't consider that. Makes sense there are some people choosing postdocs for immigration assistance or following a partner.