The source you linked to says
In a clinical evaluation, Zhejiang Orient Gene Biotech reported the tests to be 61.8% to 94.4% sensitive, depending on the type of antibody that shows up in the test results. [...] For IgM antibodies, Zhejiang Orient Gene Biotech reported an overall sensitivity of 61.8%, meaning that it may only accurately report a positive prior case of COVID-19 61.8% of the time. For IgG antibodies, Zhejiang Orient Gene Biotech reported an overall sensitivity of 94.4%, meaning that these tests should accurately report a positive case of COVID-19 most of the time.
If it were 94.4% (all the time) as you claimed in your post, it would be a different matter.
Furthermore, per recent news, the antibodies tests are "disparaged" in the US because the FDA let anyone make them and didn't request data from the manufacturers as a prerequisite for approving them:
On CNN Tuesday, senior medical correspondent Elizabeth Cohen warned that many of the antibody tests on the market for COVID-19 — the tests that show whether you are immune to the virus — are barely tested under the Food and Drug Administration’s new standards, and possibly ineffective. [...]
“The problem is, the FDA lowered the standards last month, and basically pretty much anyone can sell an antibody test,” continued Cohen. “They don’t even have to show that it works. All they have to do is say, hey, FDA, I want to sell this test and I validated it here in my city where I am. That’s all they have to do. They don’t have to show their data.”
And after the backlash, there's some sort of review announced:
[Scott Becker, CEO of the Association of Public Health Laboratories] said FDA Commissioner Stephen Hahn told him and members of his association that the National Cancer Institute (NCI) would start reviewing tests that are on the market to see if they obtain correct results. [...]
The FDA did not respond to questions for this story, referring CNN to the NCI.
A lot of the media has incorrectly headlined these news as the FDA tightening the (approval) standards, but that doesn't seem to be actually happening yet.
The WHO has now gone to some length to explain their skepticism of the (rushed) antibodies tests.
“These antibody tests will be able to measure that level of serology presence, that level of antibodies, but that does not mean that somebody with antibodies” is immune, said Dr. Maria Van Kerkhove, head of WHO’s emerging diseases and zoonosis unit. [...]
Dr. Mike Ryan, executive director of WHO’s emergencies program, said scientists are also still determining the length of protection antibodies might give a person who has been infected with the coronavirus.
“Plus some of the tests have issues with sensitivity,” he added. “They may give a false negative result.”
Earlier this week, WHO officials said not all people who recover from the coronavirus have the antibodies to fight a second infection, raising concern that patients may not develop immunity after surviving Covid-19.
And from that earlier coverage:
A preliminary study of patients in Shanghai found that some patients had “no detectable antibody response” while others had a very high response, said Dr. Maria Van Kerkhove, WHO’s lead scientist on Covid-19. Whether the patients who had a strong antibody response were immune to a second infection is “a separate question,” she added. [...]
Ryan said there are questions about whether the virus can reactivate after a patient recovers and tests negative for Covid-19.
So it's not the case that all such tests are flawed but that governments seem to pin a lot of hopes on them in terms of reopening their countries etc., which may or may not turn out justified given the present level of knowledge.