「えとー、隣に人乗る時ありますけど、なんかこう前が壁じゃないですか。」
The translation in the subtitle was “Because, sometimes people do sit next to me but there’s a sort of wall in front of you.”
I don’t understand where the じゃない fits into the translation of where “because” is in the sentence either.
As the post mentioned in comments says, to understand the sentence better, simply substitute じゃないですか with です. Here じゃないですか, roughly speaking, plays a role of "isn't it?" or "right?" (it would be a negation if there wasn't か in the end of the sentence, which, in fact, is a question marker), so the second part of the sentence is a statement that asks (but rather rhetorically) your interlocutor if they agree with your or understand you.
