Quick, what security image on a valid UK passport - a thistle, a daffodil, a rose, a clover, a coat of arms (but not the same coat of arms as on the front cover), a map of the UK, a harlequin pattern, a crown, a lighthouse, a pair of bird wings, William Shakespeare, an oak leaf, a compass, a marine chronometer, the letters UK, the words United Kingdom, a Bermuda-rigged boat, a square-rigged boat, a steamship, or the holder's birth date?
It's a trick question, you'll find all of them; they changed the passport once for brexit, and again after the queen's death. And that's just one document from one country. Far simpler to just hold it to the reader and get a beep.
For another thing, if you're worried about bribed officials - it's much harder to bribe airport border officials if they're required to scan every passport into a computer, and match it against the airline's passenger list.