Because companies no longer hire, train, and retain.
That doesnt' really explain it IMO.
If, say, I have a job. First 100 applicants get to trial it to give it a go. Some of their CVs have clear typos, a couple are 5 pages long, some use Comic Sans, Times New Roman... Considering these are clear no-nos on a CV, I would expect they don't know how to write one. If they don't, do they want the job? No. But I'm still here seeing if they can cope.
It would be a nice idea to have people after vetting to do the actual job, heck, it may be done in places, but to take people straight off without whittling out the cases of definite, pure, grade A trash, you're a money sink for the company