the flash game era benefited from an era where building a PC wasn’t completely streamlined yet, and game distribution on desktop also wasn’t streamlined (early steam was reviled and most users did not like it). Steam launched in 2003, and 2005 it went to allow 3rd parties. 2005 is also coincidentally when youtube was released, which marked the start of users moving off of well established sites like newgrounds to it over time, which flash ultimately died when mobile became more mainstream and neither google nor apple wanted to support flash. down the line.
2005 also marked the release date of the Xbox 360, which realistically was the first console where indie game development took off due to the Xbox Arcade. Also notice how paid mobile games was much more regular back during there was realistically like a few mobile phones in the market(when the iPhone 3GS was launched)