Why does the speaker say "I'm sorry, but at least we know which bus to catch to get back to your place"? I mean, why doesn't he say "Bus to be catched" = bus yg (di)kejar?

See a translation

There is no grammar context. English focuses more on subjects instead of Indonesian, which focuses more on objects. It requires a shift in the way we think, thus there is no other way; We want to memorize the pattern.

"Mobil yang mana yang perlu dikejar oleh kita?"
"Which car does it have to be caught by us?" ==> grammatically correct, yet unnatural
"Which car do we have to catch?"

Now, remove the subject "we" to resemble a real life conversation a little.
"Mobil yang mana yang perlu dikejar?"
"Which car does it have to be caught?" ==> grammatically correct, yet unnatural
"Which car to catch?"