The last Terraria sale on GOG was in July 2017, meanwhile it goes on Steam sales very often. Why is that?
If you are not even willing to spend 10 bucks on this game,
which got better and better over the years and
is still being worked on, you do not deserve a discount.
I mean, seriously, you probably bought Cyberpunk 2077
for 60 bucks even though it is not even released yet, no?
(Sidenote, look at other games that got more expensive after 1.0 or so
RimWorld as an example started at 15 bucks (iirc),
is now at 30 bucks and NEVER was on sale)