Questions & Answers about qiántái zài nàbiān.
Because 在 is used to say where someone or something is located.
In this sentence, 前台在那边 means the front desk is over there in the sense of location.
- A 在 B = A is at/in/on B
- So 前台在那边 literally means the front desk is at that side / over there
You would not normally use 是 for physical location here. 是 links nouns or descriptions, but 在 is the normal verb for location.
前台 most commonly means front desk or reception desk, such as in a hotel, office, or clinic.
Literally:
- 前 = front
- 台 = platform, desk, counter
So learners often understand it as the reception/front counter.
Depending on context, 前台 can also mean reception staff or even the stage/front of stage in other situations, but in a sentence like this it almost certainly means the reception/front desk.