Потому что это Past Simple Passive Voice - страдательный залог; объект подвергается какому-то действию.
Существует два залога в английском - Active Voice (действительный залог) и Passive Voice (страдательный залог).
I make a cake - A cake is made.
I made a cake - A cake was made.
В первом варианте мы образовали из Present Simple Active Voice Present Simple Passive Voice.
Во втором варианте мы образовали из Past Simple Active Voice Past Simple Passive Voice.
Как образовывается Past Simple Passive Voice?Утвердительное предложение:
+ was/were + 
(Past Participle)
Отрицательное предложение:
+ wasn't/weren't + (Past Participle)
Вопросительное предложение:
Was/were + + (Past Participle) ?
1)
1. a.are we meeting
b. starts/ we are meeting
2. a. Is Ian coming
b. don’t think / hasn’t finished
3. a. have you seen
b. is
4. a. do you exercise
5. a. Is Tanya
b. eats/sleeps
6. a. Are Laura and Penny leaving
b. have already left
7. a. are you looking
b. am looking / have just lost
8. a. does the Eurostar train leave
9. a. are you going
b. haven’t decided
10. a. does Leo live
b. is staying
11. a. Are you having
b. have already invited
12.a. Have you been
b. still is going up
2)
1. have been
2. am having
3. feel
4. have met
5. am sharing
6. is planning
7. hope
8. haven’t been
9. are you leaving
10. haven’t you found