When the Titemark was developed, there was the possibility of filing for a utility patent, a design patent, and possibly a copyright registration of some aspects of the design. If none of these is done, the design passes into the public domain and is freely available to be reverse engineered and copied.
No one prevented Glen-Drake from seeking protection of their intellectual property. Economic considerations may have done so, but that comes with the territory for thinly capitalized businesses.
It is also possible that Glen-Drake applied for protection and such application(s) was/were denied. The result is much the same as never have applied in the first place. The design becomes part of the public domain.
Copying of a design in the public domain is legally permissible. Indeed, enabling the public to practice inventions (after expiration or lapse of a patent if one is obtained) is a fundamental purpose that underlies the grant of a (time limited) patent monopoly in the first instance. In the view of many, this last facet of the system defines the ethics of copying a design. If the design is in the public domain, it is ethically permissible to copy it in that view.
In the view of others, a more restrictive view is that it is not ethical to copy a design developed by an individual or small business, particularly one that can't afford the costs of intellectual property protection. While such a concept seem noble at a glance, it is prone to a troublesome lack of precision: the vast majority would agree that Glen-Drake is a small business in this context. But how about, say, Gramercy Tools, with a number of people on board. Then consider Lie Nielsen or Veritas: compared to many woodworking tool makers, they are pretty large. On the other hand, compared to Irwin or Dewalt, they are pretty small. Where does one draw the line? Because of the vague and imprecise nature of such a precept, it is not a common approach.
In the end, you pays your money and you takes your chances.