Why ecris and not ecrit?
French verbs have to be conjugated:
j'écris, tu écris, il/elle/on écrit, nous écrivons, vous écrivez (polite and plural), ils/elles écrivent
why cant it be you wrote a book
"wrote" is past simple
"écris" is present.
I know right it is so confusing
So it would not be pronounced as "Too ecriz un livre" (i.e. sounding out the "s" in "écris")?
Yes, it should.
There's a liason between "ecris" and "un", right?
It sounds better with a Z liaison, yes.
"You used the you form "écrivez" instead of the you form "écris"." what's the difference?
"écrivez" is the conjugated form for "vous", both the polite address to one individual or the plural pronoun to several persons.
Conjugation of verb écrire:
Why couldn't it be "Vous ecrivez un livre"?
You were given the sentence in French. It is what it is.
Why isn't it "Tu es escris un livre". Is the present tense also the progressive tense?
"Escris" is not a French word.
"Are writing" is a continuous present tense, which does not exist as a verbal form in French.
"You are writing" translates to a simple present tense "tu écris", just like "you write".