Just like every business in the world is licensed and regulated right? Except it's not.
Where are you running a business? Yes, every business in the world is regulated, and for businesses where there is high competition and temptation to cut corners, there are regularly domain-specific rules or licensing requirements in place. A highly competitive industry is by default a corrupt industry, because the more bitter the fight, the harder it is to survive without playing dirty. In many countries and many domains, regulation evidently helps with that, but if the industry is sufficiently capital-intensive, regulation itself becomes an arena for dirty fighting.
Taxi drivers are usually poor immigrants. Given sufficient desperation they will play dirty by cheating on their taxes, scamming their customers, or working with criminal organizations (to do e.g. money laundering). They do not, however, have the resources to play regulatory capture dirty game. Uber does.
The problem can solve itself with open information.
Only it didn't when they tried. Taxis are often selected in situations where you can't meaningfully discriminate between them (from a queue, or hailing). They're also heavily used by people ill-equipped to discriminate between them (tourists and drunk people). Throwing more information on them doesn't help.