Extensions are updated to keep current with current versions of software. Obsolete versions fade away just like anything else.
Adobe and Microsoft have dropped support for classic ASP.
Unfortunately it is very costly to keep current with changes in the software industry. I have thousands of dollars worth of tools that were state-of-the-art 10 years ago, but now are worthless. That's just the way it is.
It doesn't exist. There was no CS3 when older versions of eCart were written so it would have been impossible to write for it. Not much else can be said.