"were unsuitable for" is a correct and usable phrase in written English.
You can use this phrase to describe something that is not appropriate for some purpose. For example: "The shoes he bought were unsuitable for running."
These groups believed that unskilled workers were unsuitable for union organization.
Reviewers noted that its 19th-century style and format were unsuitable for conveying the postmodern fragmentation suffered by its characters.
Since the building is hemmed in on three sides on the lower floors, most of those floors were unsuitable for guest rooms, which have to have a window.
They had committed no crime, yet were detained by the immigration service in conditions the Home Office admitted were unsuitable for them.
Lenders knew or should have known that the subprime loans of the bubble years were unsuitable for many of the targeted borrowers.
I asked Carol-Lynn Parente, the executive producer of "Sesame Street," how exactly the first episodes were unsuitable for toddlers in 2007.
It was grappling with a historic question, which is why were organisations such as MI5 so adamant that gay people were unsuitable for the secret services?
"We considered that these trailers were unsuitable for showing at a time when young children were likely to be watching," the watchdog said.
"Unfortunately in this case the dogs were unsuitable for rehoming or alternative duties and so sadly, for the animals' welfare, they had to be put down".
The Union Navy ordered 66 coastal and river monitors; these were low freeboard ships that were unsuitable for high-seas action and rarely suitable for long voyages.
The race had been scheduled despite a CART official's warning that the speedway's tight corners and high banks were unsuitable for CART vehicles.
