More often than not dedicated freight flights are more hassle than they're worth to handling agents and other third parties, it's not uncommon for a handling request to be bounced back from various agents before finally finding one willing to handle it.
Most handling agents (at MAN, at least) are stretched to the limit on a good day just with their scheduled passenger flights - throw an often delayed or sporadically timetabled freight into the mix and you've got a lot of issues for your regular airline customers.
Not all that long ago people were waiting 3+ hours for baggage:
https://www.bbc.co.uk/news/uk-englan...ester-45308369
Of course, the answer is for companies to employ more staff.... But with margins being cut so fine, I can't see it happening anytime soon.