The phrase "always unable" is correct and usable in written English.
It can be used to describe a consistent state of incapacity or lack of ability to do something.
Example: "Despite his best efforts, he felt always unable to meet the expectations set by his peers."
Alternatives: "perpetually incapable" or "constantly unable".
I took to walking at dusk, looking in at windows to see families being normal, always unable to come to terms with the loss.
During the two years my tutee and I worked together, she tried to pass the English section of the G.E.D. several times and didn't succeed, always unable to write a sufficiently coherent essay.
Mandela was always unable to pin-point when he first became politicised, though his circle of white and radical friends widened after he started a part-time law degree at the University of the Witwatersrand in 1943.
Think back to when we entered freshmen year, awkwardly walking through the halls of the old building, attempting, but always unable, to avoid getting pressed between upperclassmen in the four-way intersection.
Were the Tunisian authorities always unable to identify you?
B cells are generally (but not always) unable to undergo CSR in vitro.
He is always… Unable to sleep, Albert wanders through his dark apt.
"You see the kids always crying, unable to forget the frightening things they saw.
(Actually I have always been unable to consume alcohol in a normal manner, but you get my point).
He is, for one thing, irresponsible and not always honest, unable to admit to Sophina or Wanda that he has been fired from his supermarket job for chronic lateness.
When my mother died and was sent to be cremated I had cried, ridiculously, about her teeth, which I had always loved, unable to conceive of a world where I could no longer see them.
