From the article about why there are so few left:
The Apple-1 was a reputation-building entry, but it was the Apple II, introduced a year later in 1977, that would sell in the millions and establish the company’s business. When
Mr. Wozniak was designing the Apple II, he was also handling customer service for the Apple-1, a distracting time drain.
After the Apple II went on sale, the company began an aggressive trade-in program, offering Apple II’s and sometimes cash incentives in exchange for Apple-1’s, said Bob
Luther, who is writing a book on the vintage machines, “The First Apple,” which he plans to self-publish, with help from a Kickstarter crowdfunding campaign.
In his book research, Mr. Luther called Michael Scott, Apple’s president from 1977 to 1981, and interviewed him about the trade-in program. As Mr. Luther recalled, Mr. Scott
told him, “If we had done a better job, you and I wouldn’t be having this phone call.”
There was a limit to their minimalism.