> I don't understand how postman became the tool that it is today.

You can’t have a unicorn valuation built on a simple offline client.

This is basically standard SV play book - first step is „fix“ it to have a cloud component/account. Then store some of the data in cloud only - say for example for team sharing or a „workspace“. Then make some features paid only. Then ramp up the enshitification till metrics show it’s saturated and users will bear no more