Getting into work mode

Also reading Georgette Heyer. She is delightful. But very very very hard to understand. Why does she use so much 1820s slang? Even books actually written in the 1820s aren’t written like this. It actually makes the book very difficult to read, much more so, at least for me, than something like Dickens or Proust. Example:

He was quite a pretty whip, but no one had ever seen him take a fly off the leader’s ear, or heard of his breaking a record in a racing-curricle; he rode well to hounds, without earning the title of neck-or-nothing; and while he sometimes practised single-stick in Jackson’s Boxing Saloon, or tossed off a third of daffy in Cribb’s Parlour, he was no Corinthian.

Heyer, Georgette. Cotillion (Regency Romances) (Kindle Locations 1583-1586). Sourcebooks. Kindle Edition.