A competent, bright diver can pick up a lot of fine-tuned skills from their community. They can also learn a lot from textbooks, references and the like. Thus, progressing into areas that would normally considered the territory of formal education.
Like Nitrox. Or Deco. Or whatever.
Inside that home community, getting fills and equipment, and going dives is a no brainer, because everyone in the community knows this diver and respects them.
...As soon as this diver goes to, say, Bonaire, and wants to dive the Windjammer with their measley little OW card, it's a brick wall. (let alone dive Nitrox!) For a plethora of reasons, today's diving is set up around an examination of skills via "formal training". Which makes it an obligation, not an option.
This is not to say this diver can't move to a new location, and eventually get references and bonafides from their prior dive community. This would eventually let them return to their prior elevated level of diving, and method of gaining skills, albiet slooooowwly and as a PITA. The same could be done for trips too, I suppose, but again it would be a flail festival.
In today's world, it's a neccesity, which makes it an obligation. Not an option.
All the best, James
