I mean, they kinda have. From what I can find online, the largest capacity 3.5" drive you could buy in 2014 was 12TB.
Now in 2024, the largest drive seems to be this 30TB Seagate - not quite a 3x increase, but close:
https://petapixel.com/2024/01/18/seagates-new-30tb-hard-driv...
What hasn't really moved is the price - I feel like even few years ago a £100 could get me a 4TB drive, and the same is true today, the capacity vs cost ratio hasn't really followed the same curve as it did with SSDs.