Because in English the way it's spelled seems entirely orthogonal to its pronunciation.
"pseudo" basically sounds like "sudo".
Compare to German where the way it's spelled is exactly how you'd spell it if you first heard it (and speak German). We don't drop the "p" and we pronounce "eu" as a diphthong as in other Germans words (sounding like "oi" in English).
As a German this is why I almost never misspell it in English. It looks the same as in German and is a loanword in both languages, so I tend to sound it out the German way even when thinking in English.
"pseudo" basically sounds like "sudo".
Compare to German where the way it's spelled is exactly how you'd spell it if you first heard it (and speak German). We don't drop the "p" and we pronounce "eu" as a diphthong as in other Germans words (sounding like "oi" in English).
As a German this is why I almost never misspell it in English. It looks the same as in German and is a loanword in both languages, so I tend to sound it out the German way even when thinking in English.