OTOH, the format of the biographical page of a passport is set to an international standard that all countries adhere to. US, Japanese, Kuwaiti, etc. the biographic page is written in Romanized letters, it conforms to a uniform standard, and they are all machine readable.
This saves a lot of hassle for all parties involved.
Say if a birth certificate was enough for Americans to travel to Kuwait, then by nature of politics, reciprocally, a Kuwaiti birth certificate would be good for Kuwaitis visiting the US. However, to a typical US CIS agent, a Kuwaiti birth certificate written in Arabic is hardly decipherable. Furthermore, in Islamic culture, there really is no concept of a last name, rather it's more of a chain of names tied to a tribal clan (i.e. instead of Bart Simpson, it's more like Bart-the-son-of-Homer-the-son-of-Abraham-of-Springfield)
Japan, doesn't even issue birth certificates as they go by family register system called
koseki-shohon which is written entirely in Japanese. Again, you'll get complications where if a US birth certificate is allowed to visit Japan, reciprocally something similar to that will be accepted for Japanese to visit the US. However, try to show that a
koseki shohon to an USCIS agent, what you get is strange looks because it's just a piece of notarized paper written in a language that most agents do not understand. The family registry system is very different from the concept of birth certificates, but it is common in East Asian countries that were influenced by ancient Chinese culture. Again, you have uniformity issues here compared with the East and the West which creates more problems.
Yes it is true that one doesn't necessarily need a passport for travel. There are instances like refugees, adopted kids from abroad, or even stateless persons. The downside is that because of all these instances where you can have birthdates written in Islamic date format, to countries where they don't even use Romanized letters (Chinese, Korean, Japanese, Hebrew), and everything else which isn't uniform, creates a lot of hassle.
It's much easier and the benefit of all parties involved to have 99.99% of the world get a passport which is standardized in an easy to read and understand format for international travel, and for those 0.01% can be done without one (however will require lots of time to process immigration).