Amazing theories, however, I think the underlying reasons for the how this happened are simpler (and less conspiratorial) than have been mentioned. I don't have any inside knowledge about this, but having worked in IT for years before retirement, this scenario is consistent with what I'd personally observed happening before:
1) WU sprang from a university project and was initially constructed by a small team of developers who used the available technologies to create the first instances on dedicated servers (likely some Windows/IIS/ASP given the .asp on the WXDailyHistory.asp page).
2) The then developers expanded the functionality of the site as more and more ingress stuff (PWS data, WebCams, NOAA Weather radio, etc) was added. There was likely a second team to use the PWS data as part of weather models to refine the WU-based forecasts.
3) The site continued to expand use of JavaScript and added the WU-API for additional functionality and started offering the WU-API to developers for their own apps.
4) The Weather Company buys Wunderground. TWC has their own set of developers who'd been busy with weather.com and selling the api.weather.com services to companies as a commercial product. The Weather Company is bought by IBM, and now we have 3 architectures (Watson, TWC, WU) to try an merge. Upper management wants to streamline and mandates that the old WU architecture be unraveled and functionality ported to the TWC platform. Likely, the original developers of the WU architecture/systems have left, and since the development of that was likely sketchily documented, the people to unravel how it all works have to use the code left to understand how it works, then come up with ways to make it work on a different architecture.
5) The change of WU feature set is a result of that unraveling process and the (likely) corporate mandate to deprecate the old architecture and spin down those servers while trying to keep as many features/functions active as are viable.
I've seen many times that when a company is acquired, the IT systems undergo a (usually painful) reworking as the acquiring company now has say of what should be used.