iPads usually aren't used as much for these things. They're used for browsing, streaming, gaming, reading... mostly things that don't take up nearly as much space.
It's not spite, just matching device capabilities to user needs without unnecessary upgrades that will lead to a higher price point.
I use tons of storage on my phone. Not much on my iPad. Pretty much just downloading TV shows before a flight, but 128 GB gives you plenty of hours of that.
I'd hazard a guess that people use significantly less storage on iPads than their phones. Phones get filled with photos and videos, whereas people use iPads primarily to browse social media and stream videos.