Until a few years ago Apple was shipping new Macs with 120 GB. Probably same was (is?) happening with Windows vendors. TB-level disk space isn’t ubiquitous yet.
The difference between apple products and non apple products is that you can easily upgrade them. My core i9 laptop (a cpu that easily competes with anything apple can offer, so it should be fine for heavy workloads, albeit at bateryy cost), has 5600 mhz ram speed, 7 gb / s dual nvme support, both of which upgradeable. Most folks i know with non mac laptops can at least upgrade their hard drives and often ram. Disk space and ram not an issue for non apple users. TB disk level is absolutely feasible outside that platform. You can buy 2TB nvmes capable of 5 gb / s for less than 100$ easily.
Okay but how much dedupable dependencies does the average AppImage user have across his programs? A few hundred megabytes? A few gigabytes at most? Even 120 GB is big compared to this problem.