We do have land quarantines in our state and there are penalties for breaking it. I do agree though that there is a double standard because what I saw at WDW two weeks ago seemed every bit as risky as a cruise. I suspect the hurdle for cruising has more to do with the fact the lack of hospital access at sea if people do get seriously ill onboard.
Where we are there also self isolation (quarantine) requirements if you test positive: at least 14 days, longer if needed due to symptoms. And your household members and close contacts ALSO have to self isolate for 14 days (their clock resets if they develop symptoms themselves). You're only allowed out to medical appointments. Public health contacts you each day. If you need assistance getting things like groceries there are services that can help with that.
For cruising there can also limited hospital access for ports, whether in terms of having a hospital at all or hospital capacity. For example, Skagway, Alaska does not have a hospital; this is the info from Wikipedia:
Skagway is served by Dahl Memorial Clinic, the only primary health clinic in the area. The facility is usually staffed by 3 Advanced Nurse Practitioners and 3 Medical Assistants and is open Monday through Friday year-round with limited Saturday hours during summer.[citation needed] The clinic also operates after hours in emergency situations. The borough is also served 24/7 by local EMS. Individuals in need of dire medical attention are transported by air via helicopter or air ambulance to Bartlett Regional Hospital in Juneau (an approximately 45 minute flight). Whitehorse General Hospital in Whitehorse, Yukon is the nearest hospital to Skagway that is accessible by road (an approximately 2 hour drive).
I do think for cruising to resume they are going to have to do quite a combination of things, from testing [and that may be daily testing now that it appears there are rapid tests that could make that feasible] to itineraries that are more conducive to managing an outbreak should it happen [or as mentioned short enough that an outbreak would be somewhat self-limiting].
SW