Yes I understand that it's likely that squatters would've taken this instead. But instead of coming up with a solution for that (like, if you don't use it for X amount of time, then it's lost), they instead decided "why don't we just take that money"
The squatters are actually better in some cases. If they're selling a non-premium domain that you can renew cheaply, the up front price can be more tolerable than the long term cost of a premium domain.
It looks like the premium domains for .zip are about $550 USD on Porkbun. I'd way rather pay $5k up front for a .com compared to $5.5k over 10 years for a .zip.
Okay, now come up with a definition of "use" that effectively eliminates squatting-for-profit that doesn't also eliminate legitimate uses for having multiple domains that don't look like they're "being used"