The number of users in lemmy is so low compared to reddit. Those who buy this app are way less here. In reddit there were 100k+ downloads. Here it is not even going to be half of it. So price change can be justified.
One point I like to say is yeah this price is too high for some third world countries. Region based pricing should be there. 20$ here is 10% of my income (entry level job). So it will take time for me to buy the app. Until then i support the ad driven model. I am getting far better user experience with this app than all other lemmy apps I have tried.