There are developers out there who were smart enough to register as VST2 developers before Steinberg stopped that. Any one of them would now have a fairly trivial time releasing a WRAPPER that could easily allow VST2 plugins to be loaded in VST3 hosts. If any of them cared enough to do so.
This sounds like it would eliminate your concerns, as it would mine: I’m a developer planning to release a host, and being unable to support VST2 puts me at a significant disadvantage (forever) next to any of the existing DAWs that had VST2 support. Only because I am doing it later. All of those developers, of Reaper, Cakewalk, FL Studio, etc., etc., etc., can continue to support VST2 as long as they want, and none of them - besides Steinberg - would ever have any reason to drop that support.
There are many VST2 plugins that people still use that have never been released as VST3, and others for which the VST3 versions still have problems. The market, producers, developers, musicians - none of those people prefer not to have the option to use VST2. Only Steinberg.