I think that you have made all these problems up in your own head. It sounds like you have never hired some one on a maternity contract?
No, I haven't.
Why would I make it up
I worked for ten years in engineering firms, witnessed more than a few women have maternity leaves, and had 2 myself, and not once were they covered with a temporary worker.
Outwith IT / software, I've only ever worked directly with one contractor, and they were desperate to have him permanent but he was adamant he wanted the winter off to go to his holiday home.
Why is it so hard to understand that some jobs can't just hire joe bloggs off the street
all of our systems were custom built for the company (in both places I worked at). It took me 3ish months just to get through all the procedural and process documents. And that's before you have the chance to learn the multiple products, all with complex sets of requirements. Yes, I still contributed during that time, but both times it was about a year-ish until I found my feet and actually ramped up to 100%.
Having a long line of highly qualified and experienced temporary workers desperate to apply is probably a luxury afforded to bigger cities. You release we're not all in London? Where are all these radar engineers desperate for a 6 month contract in Yeovil? Blackburn?
BUT that's not even what we're talking about. We're talking about small enterprises that don't want to hire a temporary worker for a full time role.
You maintain it's so easy to hire maternity cover, and apparently everyone is doing it, so if I was op I'd have applied to cover someone else's maternity. Problem solved.