You have to try to place yourself in 1981 to see it all in perspective.
In 1981 8" floppies were still a thing, but quickly being phased out by the 5.25" floppy. The former had storage capacity from 90 Kb up to 1.2 Mb, but that amount of data on one disk was deemed "unncessesary". The 5.25" floppies, on the other hand, started with 320 Kb (which sometimes was distributed on each side of the floppy) and went as high as 1.2 Mb as well, though that wasn't really a thing until the late 1980s. (Games and software needing 6 floppies was also not really a thing until the late 1980s, and most of the time they were on so many floppies for the sake of backwards compatibility. Remember, more than 95% of PC games made in 1989 could be booted up on the original IBM PC released in 1981.)
This, of course, assumes that all floppies were equal across all platforms. Wrong. Each computer platform not only had a different format layout for their floppies, but also a different OS to read them, meaning that sometimes you couldn't tell for sure what computer a floppy was being used on. So in, say a company with 100 employees that relied upon computers, it could be a full-time job just keeping track of all those floppies...and more importantly, replacing them, as they were flimsy as fuck and very prone to data loss.
Meanwhile hard drives had been a thing for 25 years, with the first 5 Mb hard drive ever made being the size of a closet and about half the weight of Poland. Yet people immediately saw the benefits of having hard drives, but the problem was getting them small enough to fit into a personal computer. That drive shown in the ad is one of the first models for personal computers and a monster even by 1990s standards, but it worked and it replaced a literal army of floppies, probably twice its total storage capacity.
I'd be willing to bet that despite the initial cost, a hard drive would have paid itself off in the long run at the very least.