The barrier to entry was low early on. Developers openly shared information as the Internet gained adoption. View source meant an inquisitive person could teach

The barrier to entry was low early on. Developers openly shared information as the Internet gained adoption. View source meant an inquisitive person could teach themselves new tricks. Web development in its infancy was simple so a whole generation of developers could learn as the technology improved. As a developer in the 90s and early 00s it wasn't cheap or easy for everyone to get Visual Studio/Delphi/Borland C++ Builder, not to mention obtaining the knowledge to drive those tools effectively. Web development might be more difficult today but for a decade or two it massively smashed barriers to entry.