I'm enjoying it. But why is so much it fiction than Fact?

Yes, they have to make characters attractive to our contemporary standards, and perk up their lives to keep our interest. Much as loosely scripted 'reality shows' condense hours of tape into all the 'good bits' , there have to be attractive people doing interesting things, even bringing in drama from the servants, to keep it interesting. No one really leads a consistently interesting life, long long stretches of a monarch's real life were dull, mundane. A pretty young woman becoming the most famous Queen hooks the viewers right away. Hopefully.

According to Victoria's biographer Lady Longford, those letters were dictated by Lehzen and Victoria knew whatever she wrote at Kensington would have been read by her mother; she says their first encounter (1836) was in fact a bit of a disaster because he fell ill, vomited, wanted to go to bed at ten and one time he also slipped on the dancing floor and fell backwards. Plus, at the time he was not good at riding or any sport and he was a bit chubby. His family took care of most of it before trying again to convince her to marry him.

You can find it here: https://www.youtube.com/watch?v=bFLyOZc5B1k

I don't get it, because "truth is stranger than fiction."

And neither was Victoria.