Why are they magically discovered then in only last century? There can be many motivations for this.
"Dinosaur" bones sell for a lot of money at auctions. It is a profitable business. There is pressure for academics to publish papers. Museums are in the business of producing displays that are popular and appealing. Movie producers and the media need to produce material to sell to stay in business. The mainstream media loves to hype alleged dinosaurs finds. Much is to be gained by converting a bland non-dinosaur discovery, of a bone of modern origin, into an impressive dinosaur find, and letting artists' interpretations and imaginations take the spotlight, rather than the basic boring real find. There are people who desire and crave prestige, fame and attention. There is the bandwagon effect and crowd behaviour. And then there are people and entities pursuing political and religious agendas.
Wow.
Paranoia will destroy ya.
I bet you look under your bed at night for ancient aliens. :<(