I think lots of factors like this affect activity on the Destruction forum:
Destruction is the least competitive so attracts little of that player base/mind set with essentially one cookie cutter list in ironjawz for most of AoS 2.
Very low variation in army construction with factions often having very few choices e.g IJ/BS/SoB and even GSG just got pushed into narrow subfactions with little variation due to keyword bingo.
Overall army design often provides little longevity in playstyle and there’s far too much so-called “fun” being used in the design process which just seems to equate to low-power gimmicks.
If you compare releases, SoB is so low effort compared to non destruction factions. One sculpt, minimal rules, more gimmick. There’s almost nothing to discuss/solve. Then there’s the ridiculously overcosted Kragnos who again has an over complicated MW on charge rule but really is another watching paint dry design who was randomly inserted for sales. Again adding very little to most destruction armies.
Kruleboyz - we have a new SUBfaction being released for destruction rather than a proper faction, so is already less likely to attract the attention of new players who were not interested in orruks.
Lots of this stuff adds up and I reckon puts people off destruction. Maybe Kruleboyz will be different?