Having a 10GbE port obviously has LAN usage in mind before WAN. Even for proclaimed multi-gig ISP connection, usually the benefits isn't to reach that bandwidth for a single stream, but more meaningfully a less constrained outward pipe for an organisation with dozens of outward streams or more.
In the case of Macs with built-in >1G network, it happened as early as the G5 / Mac Pro 1,1 days where you could put in network cards; in fact Apple sold those themselves, dual fibre channel cards with SFP was standard issue since that is what was used to connect to Xserve RAIDs.
Afterwards the Trashcan Mac Pro loss that 10G built-in since it got Thunderbolt. Only until the 2018 mini where you could start to config 10G built-in, then the iMac Pro 2017, Mac Pro 2019, and Mac Studio have it standard-issue.
The point is, looking at the trajectory of 10G support on Macs, it was clear to be meant for LAN usage. And it pretty much was exclusive for the higher end of Pro Macs since in the beginning it was meant for professional environment with infrastructure to support it.
Lately (say last 5 years) 10G network appliances became more budget friendly, so you see even home(lab) users are enjoying that. Or video editors with no intention on building network infra, but still need basic >1G speed to his servers then he can use a direct 10G connection from a Mac to a NAS without even a switch. For a base mini with even the recent price cut Apple still offers the option of 10GbE is actually a really nice a flexible way for homelab users to maximise the mini's potential, or for some others to "future proof" their mini.