The Many Benefits of a Second Passport
The rise of nation-states, nationalism, and especially World Wars I and II made it essential for international travelers to present passports when they entered a country.
Today, governments increasingly use passports as instruments of coercion. For instance, U.S. citizens can be denied a passport simply for owing money to the IRS or in child support payments. Even U.S. citizens living abroad must pay tax on their worldwide income. If they fail to do so, the government can decline to renew their passport.
Since governments use passports to enforce coercive laws and regulations, it only makes sense for those with the means to do so to acquire a passport from another country.