I don't know if new members for forum is any guide but there has been a bit of a reduction over time.
I think you might be misreading the chart. I don't think there's been much a reduction. Rather, the sign-up rate has fallen back to its normal background rate, but unlike previous years there hasn't been anything in a while to temporarily boost the rate.
The only question is how to explain the spikes in previous years. That is, what goosed the rate temporarily? I think that's pretty easy to explain:
- The big jump to about 500 / month in the 2nd half of 2012 is undoubtedly related to the release of Laz 1.0. Within a year the rate had fallen back to its background rate since no other major release had been made in the meantime.
- The jump in late 2013 and into 2014 is probably due to the runup to Laz 1.2 and its release.
- What about the enormous jump in the first half of 2011? I suspect this has something to do with the excitement over the expansion of FPC to other platforms, particularly to iOS with FPC's ObjectiveC1 modeswitch, and this carried over to Lazarus. Delphi's support for iOS came at the end of summer 2011 and you can see what this does to Laz signups: they're back to the background rate.
Interestingly, subsequent releases of Laz 1.4, etc. have had no appreciable effect on the sign-up rate. But perhaps that's what one would expect - they're not the milestone releases that 1.0 and 1.2 were.
So you can see the pattern: users get their hopes due to new developments in the Laz project, resulting in a temporary increase in the sign-up rate, then a fall back to the background rate once the euphoria wears off (eg, with iOS, where nothing came of it). With nothing new I wouldn't expect spikes any time soon.
So it looks to me like interest in the Laz project is fairly stable now, although if the total number of developers of all kinds has increased, then a flat line is actually a decrease in the percentage of all developers using Lazarus. Apple signed up 3 million new developers last year. Lazarus? Looks like about 2,000. So that's 3 orders of magnitude difference.