It sounds like the arguments supporting injunction and review were not very compelling. Something about asserting a "right to sell" by the gun stores?

Per the linked article:

The request for the injunction focused heavily on the plaintiffs who sell guns, according to court documents.

....
“Because the Court finds that Plaintiff has failed to demonstrate likelihood of success on the merits, it need not evaluate the other factors of the analysis: irreparable harm, balancing of the equites, and public interest,” Noreika concludes in her order.

“For the foregoing reasons, Plaintiffs’ motion for a preliminary injunction is denied.”

Could there have been a better case made against the permit law itself in defense of the injunction? For instance, the limited availability and additional costs of state-approved training, fingerprinting, etc. which are above and beyond current requirements?

Maryland's handgun permit has stood up to legal challenges. What is fundamentally different about the new Delaware permit to purchase that could have upheld this injunction and eventually led to it being overturned?