And yes, most of those extra letters used to be enunciated. Try listening to a reading of Chaucer in the original Old English and you will see what I am saying.
In some cases, the letters are left over from when we stole the word from another language but didn’t quite know what to do with it.
And then there is verbal shorthand such as British place and family names:
“Fanshaw” (Featherstonehaw)
“Lester” (Leicester)
“Chumley” (Chomendely)
“Tackleston” (Tacolneston)
“Hazebrugh” (Happisburgh)
“Trosley” (Trottiscliffe) and many, many more.