You're probably remembering flash games fondly. Flash as an enabler of creative teenagers. But back then flash was used for a lot more; it was pretty common for entire websites of businesses to be built as terrible flash apps. Want to look up a local business's hours, menu, phone number? You had to have flash installed, had to navigate whatever harebrained animated UI the owner's nephew had created, and hope it didn't crash your browser. Never accessible, never performant unless you had a very powerful computer, and it would always spin up your fans. Less savvy users wouldn't be able to identify the problem and would leave flash pages open in the background, then conclude they had to buy a new computer just to get work done again.
It was a binary plugin with supported platform at the whims of Adobe, it often had security bugs and sandbox escapes, it had bad performance and killed mobile battery.
For the the web standards have replaced the use cases have improved the situation