Because an actual fix would have been more complicated than you think. And, yes, as immediate neighbors to Point Roberts, which I have visited several times, us BC residents are very aware and sympathetic of that city's plight.
First, let's be clear, the management of border crossings wrt US enclaves has not been free of stupid moves on the Canadian side. I remember a reading about a Canadian woman foraging (for mushrooms?) crossing the border in Alaska by a few meters and getting whacked with 14 days of quarantine on "re-entry".
Second, the main problem with Point Roberts isn't US-to-Canada travel. Nor, really, it is US-to-US travel. Your map leaves out that it's a short, 20 km, crossing on fairly sheltered water to get to Blaine, WA on the continuous US. It is certainly not about goods and supplies as commercial trucks have been considered an essential service, along the full border, from the start of the pandemic.
No, the real problem is that Canadians, who drive a lot of Point Roberts' economy can't visit anymore.
Since mid-summer (this article was in Nov, 2020), the Chamber of Commerce said the community has been paying $40,000 per month for a twice weekly boat shuttle to Bellingham.
Residents have five hours to shop before returning home but Calder said the round trip can take nine hours and the sailings are often cancelled due to weather.
Meantime, Calder said businesses in Point Roberts are down 85 per cent because the Canadians who own 75 per cent of properties are currently shut out of the community.
Now that the border is being cautiously reopened US-to-Canada, these restrictions are even lessened, for Point Roberts residents (Aug 1, 2021 article):
As of Monday, fully vaccinated Americans are able to enter Canada and even skip quarantine. But residents of Point Roberts, Wash., Hyder, Alaska, and the Northwest Angle in Minnesota will be allowed to enter Canada regardless of their vaccinated status.
All three communities are cut off from the rest of the U.S. because of the placement of the border.
The Canadian Border Services Agency says residents of Point Roberts may enter Canada regardless of their vaccination status to "carry out everyday functions and access goods and services within their neighbouring Canadian communities."
But Canadians are still not allowed to visit Point Roberts, making this somewhat moot:
So far, the U.S. has announced no plans to open its borders to Canadians, whom businesses in Point Roberts rely on. The community's economy has nearly completely crumbled, shrinking by 80 per cent.
At a guess, a more useful approach, from the start, would have been to allow border crossings as usual, with normal border controls, both ways, between Point Roberts and Canada. But enforcing quarantines USA to Point Roberts. That would have kept Canadians safe and Point Roberts prosperous. But it would have been a bitter pill for US sovereignty to contemplate, which is why it was never, to my knowledge, considered.
Hyder, AK and the Northwest Angle, MN are different in nature because they are essentially inaccessible except by air from the US, unlike Point Roberts where boats provide "easy" access. So there was never much risk of US-to-enclave covid spread and then enclave-to-Canada spread. As a result, rules have been more relaxed for them since October 2020 and they were never real destinations for Canadians anyway.
FWIW, minus any problems accessing the US itself, the folk at Blaine, WA - the East side of that line on my map - have had essentially the same problem, though at a hopefully somewhat lower scale. They can access the US just fine, but relied on lots of Canadian customers. The thing is, this part of Washington is fairly rural and cheap and is right next to some of highest cost of living cities in Canada so in normal times the economics favor cross-border integration.