ActiveX was relatively open-ish. Back in the days young me used a Visual Studio 6 off of eDonkey to develop applets in VB6.
The problems were that:
- unlike modern compiled code for the web - WASM and transpiled JavaScript - Java and ActiveX got executed with host privileges which made both an incredible entry point for malware such as "dialers" and early viruses.
- many corporations and governments (e.g. Korea [1]) built their stuff in ActiveX or mandated its use in actual laws and regulations, while only MS Internet Explorer ever implemented ActiveX out of said security reasons.
- many corporations and governments only ever coded and tested against IE6 which meant that their sites and products were dependent on IE6-specific quirks
