The latest and greatest

I think you have two things going on with the LS50 that are causing them to come up for sale in greater numbers.  First, the LS50W appears to be an improved model...which in many people's minds devalues the original LS50.  Second, the LS50 purchase price new seems to have dropped from $1500 to $1000 https://www.crutchfield.com/shopsearch/kef_ls50.html
which means owners of LS50s thinking of selling may want to sell before the price drops even more.

As for LS50Ws...no doubt that at $2000 there are a lot of great choices and people who bought them are probably a little concerned seeing how much the price of the LS50 dropped.

The LS50s don't do everything perfectly.  In my opinion if you want scale and dynamices, there are better choices at $1000...but if you have a small to moderate size room and you want tonal purity and great imaging, the LS50s remain a great choice.

The LS50W (for Wireless) is an active speaker, so you get an amplifier in the bargain.

Yes and now that the ls50 w is $1200 more than the non amplified version it may not be perceived as such as bargain. 

More generally, technical progress is slow. As for source technology, we have witnessed two breakthough moments. The first was the introduction of the vinyl lp that made 78’s obsolete. The second was the cd and the digital technology behind it, which made vinyl obsolete (whatever audiophiles may want to believe). With the cd, we have probably achieved sonic perfection. At the time, this was also the limit of what was technically possible. These days much higher resolutions are technically possible, but the question is if (unlike our dogs) we can actually hear the difference: human hearing is not that good.
A similar plateau has been reached with amplifiers. Ever since output transformers were largely abandoned decades ago, amplifiers have reached a state of sonic perfection where technical improvements were still possible (current ampifiers do measure better than those from the seventies), but again the question is whether we can hear those improvements. A good example of the technological continuity that was inaugurated is Quad’s current dumping technology, first presented in 1975 in their 2x100 watt 405 model, and still the basis of their current 2x140 watt Artera model. The biggest benefit of advancing technologies has been higher output powers for lower manufacturing costs.
With speakers there has not been such a plateau, since speakers are still far from perfect. Slowly but steadily speakers have improved, with new materials, new computer simulation design technology and new manufacturing technology. But progress is slow. I am now listening to my Harbeth P3ESR desktop speakers, proud descendents in a direct line from that remarkable BBC design from the seventies, the LS3/5a. I still have both models, so I can compare: the new Harbeth is much better, but it is also clear that they share a family resemblance. Progress has only been incremental. The same can be said about my main speakers, now the Quad 2805 electrostats, but the ELS57 before.
My hunch is that the biggest jump in domestic audio quality will be the adoption of more advanced dsp technology in active speakers, both to improve on traditional crossover technologies, and to equalize room effects. I also expect one other trend, even if it will do nothing to improve sound quality: reduction of energy consumption. Here in Europe, concerns about climate change have not only introduced mandatory specifications for energy consumption by refrigerators or vacuum cleaners (our new one only consumes half of our previous one, but is also much better), but now also for televisions. High end audio is obviously a much smaller and hence less important market to address, but the writing is on the wall.