This is most likely due to larger player pool size for LoL - it is more popular than DOTA2 in China, so the effect is less noticeable. LoL was not really popular before around 2015 in China but then exploded in popularity and there was an influx of new players to the Chinese scene. There're still Korean imports in most champion teams (e.g. iG, Edward Gaming, etc.) but Chinese scene still maintains a large pool of players. SK won in 2017 btw.curious, League of Legends is doing better. From start of gaming restrictions in 2019, here's the championship results in 1st,2nd,3rd format:
From start until 2016, it was Korean dominated. 2017/2018 were Chinese wins.
DOTA2 has a smaller player base, so the effects began catching up faster than for LoL. Still, the noticeable drop began only in around 2022 and probably the harsher restrictions introduced 2021 (3 hours a week total instead of 1.5 hours a day on weekdays) accelerated the process plus this coincided with the retirement of most of the LGD's (China's top 1 team from 2017 up until now) star roster which emptied the scene further.
It will be interesting to see the results for this year's LoL WC.