GW's social media presence and advertising is finally a thing. I believe this is the main reason for the increase in sales. GW is releasing kits with fewer models for higher prices. The Primaris, DeathGuard and now Custodes all have boxes which have only 3 models in each. Most releases consist of a large model or two, and maybe one or two squads/warbands. Clearly, kits like Magnus, Gulliman and Mortarion pay significant dividends over kits like the Orlock gang.

They have also diversified their income streams. We now have multiple boardgames (necromunda and Shadowspire for example) which help reduce dependence on the main line. GW have made a lot of shrewd moves, which has helped them repair several years worth of damage. 8th Edition is being supported for tournaments and they're actively tweaking the system in response to feedback. How well they are doing at these is subjective, but the very fact they have been making effort is a huge difference.