There is more to writing well than learning the difference between "your" and "you're".
Should you vary your sentence structure? Yes, but not by using a long, long “that clause” as a subject, or any long, long string of words. Subjects should be short and concrete.
The Penwith Moors’ proposed designation as a site of special scientific interest by Natural England is to protect the ancient landscape and ensure its rare habitats, flora and fauna can thrive in partnership with local farmers. (15-word subject. Are the “habitats, flora and fauna” in partnership with local farmers? Or is Natural England in partnership... etc? How about “intended to protect”? And who is doing the proposing? The Penwith Moors or Natural England? West Penwith is pictured.)
Natural England's proposed designation of the Penwith Moors as a site of special scientific interest is intended to protect the ancient landscape and ensure its rare habitats, flora and fauna can thrive, in partnership with local farmers. (Still a 15-word subject, but we have Natural England proposing to designate the Moors.)
Hiring as few people as you can get away with, and spending the bare minimum on them, is counterproductive. (17 words.)
Sometimes it's better to make your subject "it": It’s counterproductive to hire as few people as you can get away with, and spend the bare minimum on them.
It's better than using gerunds as subjects, anyway (hiring, spending).
This isn't a howler, but I'm tired of paragraphs that start: Part of the reason for [X phenomenon] is blah blah… “Part of the reason” is a weak subject, and doesn’t invite you to read on. Better to start with X phenomenon.
But sometimes a long subject works:
A convicted housebreaker and killer turned soldier, courtier and magnate in the North of England can be identified as the author of the 14thC masterpiece Sir Gawain and the Green Knight, a philologist says. (@history1st)
This is the Time magazine technique of “backward ran the sentences until reeled the mind”.
REASON, FACT, WAY
Use a noun as your subject. Not "why" but "the reason", not "that" but "the fact that", not "how" but "the way".
You may have been told not to use "the reason why" because it's a tautology, but we need a noun here and "reason" will do. But weren't you told to prefer the active to the passive? "We still don't know why... etc." Then we peak on "Rome". If you feel "we" is too vague, how about "Archaeologists still don't know..." (An editor told me never to use "we" or "you" because it's not clear who's being talked about – and he had a point.)
How physical places can enhance or damage our health may sound unscientific, but Esther Sternberg constructs a convincing argument in this book. (What sounds unscientific? How about: The idea that physical places...? And hang on, aren't all places physical?)
Was there a more exciting time to be in science than as the 18th century melted into the 19th? (New Scientist, 2009. Was there a more exciting time to be in science than the period when the 18th century melted into the 19th?)
Making the hoax more credible was that, during the previous year, hundreds of homes in the region had been damaged for real when the Ochoco creek flooded. (time.com. Make it "the fact that".)
Coronavirus has brutally reinforced that it pays to be privileged. (...the fact that...)
You cannot play online multiplayer because of how your Microsoft account is set up. (Make it: “because of the way...”.
That he survived was partly due to his charm and wit. (Your subject is “that”, your verb is “to be”. Dull! "But he couldn't have survived without his charm and wit.")
That relatively few now claim asylum is because the vast bulk of the persecuted are ignorant of their right to it. (Relatively few now claim asylum – because most of the persecuted are ignorant of their right to it.)
That she survived with little apparent damage and went on to achieve literary renown – along with editing two editions of the Oxford Companion to English Literature, she has published a number of respected novels and a biography of Arnold Bennett – gives us some reason to hope for the future of Emma Evans, her narrator in this early novel. (Goodreads review of The Garrick Year, Margaret Drabble (A 40-word subject, containing a parenthesis. And you mean “the fact that”. Or how about "Her survival with little apparent damage and later literary renown..." Now we have two nouns as a subject: survival and renown.)
That the Denisovans were discovered in southern Siberia but contributed genetic material to modern humans in SE Asia suggests that their population may have been widespread. (Times 2010. The fact that...)
That seas marbled by oil slicks make breathtakingly beautiful images doesn’t neutralize them as records of devastation. (The fact that...)
That the rules of grammar were ignored by the Barbarians was not entirely unsuspected. (The fact that... Unfortunately, "The Barbarians's ignorance..." doesn't have the same shade of meaning, and despite the old Punch joke there's no such word as "ignoral".)
More here, and links to the rest.