Why does the Royal Family dress conservatively?

Lately I've been wondering why Kate Middleton and Meghan Markle suddenly changed their style when they joined the Royal Family.

Before she was married to Prince William and joined the Royal Family Kate Middleton was so stylish and had a fun loving personality. She wore the type of outfits you'd expect any young 20 something to wear. She looked easygoing and as if she was a free spirit. You can see the evidence of this in the image below. 

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 Source: https://www.mysanantonio.com/entertainment/celebrities/article/Kate-Middleton-Meghan-Markle-old-photos-12407986.php?ipid=artrecirc 

Then of course, she met Prince William, started dating him, became engaged and her style completely changed and became dull and drab. The mainstream media (MSM) however will still say she is a style icon and looks fabulous but really it's like she gave up her personality when she joined the Royal Family or PR (post royalty).

You can see this in her wedding gown. Now of course, everyone gushed over it but it's absolutely hideous and makes her look like an old lady. It doesn't reflect her genuine personality.

Source: http://people.com/royals/pippa-middleton-wear-two-wedding-dresses-kate-middleton/

Most 29 year olds would not wear dresses such as the two that she wore. They are extremely conservative and don't reflect the personality we saw in earlier images. Nor do her current outfits.

Source: https://www.aol.com/article/2015/12/21/2015-wrap-up-a-year-of-style-with-kate-middleton/21286539/

In recent pictures she is emulating the Queen with her coloured trench coats and hats. She also wore a maxi dress and it doesn't seem like Kate's style. Here is another throwback image to before she became part of the Royal Family. She dressed as if she was having fun and was so much more laid back whereas now she dresses extremely conservatively.

Source: https://www.harpersbazaar.com.au/celebrity/kate-middleton-style-before-duchess-12387

 A similar style transition/evolution has happened with Prince Harry's bride to be Meghan Markle.

Here she was before she started dating Prince Harry.

Source: https://www.thesun.co.uk/tvandshowbiz/2451704/meghan-markle-prince-harry-age-suits-actress-parents/

She also had a fun style and was casual. She liked sparkly clothing. Now that she is engaged to Prince Harry (and due to marry him on the 19th of May) things have changed and she's way more conservative.

Source: https://www.express.co.uk/life-style/style/919404/Meghan-Markle-pictures-style-fashion-Prince-Harry-Meghan-Markle-pictures

Now that she is engaged to Prince Harry her style was changed as well and she dresses in trench coats, much like her sister in law Kate, and the Queen as well.

 

So my question is, why do members of the Royal Family have to dress conservatively? Why can't they just be themselves?

Basically it amounts to this. The Royal Family are dictated to by Queen Elizabeth. She dresses conservatively and favours a corporate look, so therefore her underlings like Camilla, Kate and Meghan do as well. When the Queen no longer holds her title and Camilla is Queen Consort to Prince Charles things might change but until then there is a strict dress code that is tighter than the toughest of workplaces. That is why we never see anyone in the Royal Family wearing short skirts and dresses, or baring their arms like members of other Royal families around the world do.

Unlike Queen Letizia of Spain, Kate and Meghan would never be allowed to wear an outfit like the blow.

Source: https://www.harpersbazaar.com.au/celebrity/why-british-royalty-dresses-so-conservatively-15107

Things may of course change in the future, but for now conservative dressing is expected of the British Royal Family. It all sounds a little unfair really and I wonder if the Royal Family members are allowed to dress casually when they're at home and out of the public eye, or if they must always uphold a certain dress code.