The author doesn't even seem to know what a rave is, most likely they aren't in decline at all. They're talking about formal, permanent dance clubs shutting down for economic reasons. Raves are mostly an underground - often illegal or questionably legal - impromptu one off event, organized through word of mouth and social media on an invite only basis. There is almost no way to get statistics on them because they are…
In the UK, where I believe the word originates when applied to late night electronic music events in the mid 80s, the term meant an often unauthorised event in a field or industrial site.
Perhaps it was the noise menace, or perhaps people dancing in a field fuelled by MDMA caused a big deal in alcohol duty revenue for the government, but raves became highly regulated with the 1994 Criminal Justice and Public Order Act. Illegal raves were clamped down on by police with a fierce intensity. This essentially pushed the music back into clubs, where people could be taxed more easily. This ended the original race scene. By the late 90s the term was anachronistic in the UK. In the 2010s certain dance subcultures, drum and bass springs to mind, started becoming known as raves again, but these were anything from club nights to outdoor festivals. Quite unlike the earlier usage
It appears that your usage mirrors the UK rave scene from the late 80s to early 90s that died out, and the author has a broader usage that is in use today in the UK.