It's a general tendency I have noticed on LabVIEW forums, although maybe less so on the NI forums. I also signed up at the German LabVIEW forum and while 5 or 6 years ago you had every day several new topics varying from the newbie question of how to do a simple file IO operation to the advanced topic of system architecture and interfacing to external code, nowadays it is maybe a tenth of that with most topics ranging in the more trivial category. The German forum had and has a somewhat broader target range since it was equally meant for beginners and advanced users while LAVA started by the nature of its name as a forum for somewhat more advanced topics, although I would like to think that we never really gave a newbie a bad feeling when posting here, as long as that person didn't violate just about every possible netiquet there is. The German forum may have one additional effect that may contribute to it getting less traffic and that is that English has also in Germany got the defacto standard in at least engineering.
But without having any numbers to really compare I would say that the German forum and LAVA have seen similar decay in number of new posts and answers in general. And yes I have been wondering about that. Where did those people go? I feel that some went to the NI forums as they got more accessible over time but I do think that a more important aspect is that LabVIEW has gotten in many places just one of many tools to tackle software problems whereas in the past it was more often THE tool in the toolbox of many developers. That is probably a somewhat jaded view from personal experience but I certainly see it in other places too when I get there during my job.
And Shaun definitely addresses another point when he mentions that LabVIEW innovation has slowly been getting to the point of stagnation in the last 5 to 10 years. That would hurt specialized forums like LAVA or a local forum like the German forum most likely a lot more than the NI forum, which catches most of the more trivial user questions of how to get something done or about perceived or real bugs. I'm not sure in how far the NI forum has been seeing a similar slow down. Personally I feel it might have been getting a little less active overal in comparison but what is more apparent is the fact that there too the general level of advanced topics has been slowing down, which would be in accordance about little to no innovations in LabVIEW. The interesting things have been discussed and brainstormed about and very little new things got added that would spur new discussions. What is posted nowadays is mostly about problems when using LabVIEW or some hardware or how to get a simple job down quickly!
Is LabVIEW dead? I wouldn't feel so as I still see it used in many places but the excitement about using LabVIEW has been somewhat lost by many. It's a specialized tool to do certain things and in a way the only one in town doing it in this way, but by far not the only one you can use to do these things. In fact there have been many new and not so new possibilities about doing it (I see for instance regularly situations where people have decided to use Python for everything even the UI, which is not something I would easily consider) and the general target has been shifting too. If you want to do internet related stuff then LabVIEW is definitely not the most easy solution and also not the most powerful one. Engineering simply has been getting a lot broader in the last 10 years and while measurement and testing where you directly tinker with hardware and sensors still is quite important, there has been another big market developed that has very little to do with this and where the qualities of LabVIEW don't shine as bright or even show nasty oxidation spots.
Maybe the fact that LabVIEW always was designed as a closed environment with very limited possiblities to be extended directly by 3rd parties has hurt it to the point of being forced into the niche market it always tried to protect for itself. It will be interesting to see how NI is going to attempt to fix that. The stagnation in LabVIEW development is something which supposedly happened because they focused the energy on a fundamental redesign of the LabVIEW platform, which has dragged on longer than hoped for and claimed more resources than was good for the existing LabVIEW platform.