It was big, supported platform supported by big company. Until it was not. Overnight, you were told to rewrite all your sources to new, shiny language, also called VB.
Basically, VB1-VB6 were compatible. You made app in any of them, it required only small changes to build with never version, no big deal.
However, 2000 called and Microsoft came with new version, Visual Basic Net. It changed syntax, class libraries, everything. With the old VB, it had only name in common. It looked similar only on the surface (both are Basics, anyway). Sure, they fixed lot of warts, but broke many existing apps, that were in the maintenance mode for the time. If you relied on VB6 apps, and VB6 runtime had problem with new version of your OS, you just could not upgrade without expensive rewrite.
The message is: just because the language or platform is supported by big company, does not mean, that it is safe for your business to build your apps on it. On the other hand, ten years ago I took the risk to build an app in Python. At the time, it was little, unknown language (especially in the MS world). The app still works reliably today and is buildable (only .pycs were deployed) by modern Python.