Maybe it's a trick question. Maybe your teacher was referring to the front side bus (computer) at the front side of the bus (vehicle). Therefore the answer would be, "Why does someone have a computer at the front of a bus?".
Ignore those guys that's just the way they are when they come down, or when they don't know the answer. They tried really hard, they went and got you the WikipediA answer for you. When that didn't answer your question they turned in to... I mean continued to be little wanabe children.
I don't know if you are looking for the technical reason for the front side bus or the trivia answer as to why it's first name is front. I don't know the trivia answer, but long ago processors only had one inter face to the outside world and that served processors fine before they started processing information faster than the speed of light (well not really, but it seems light it.) Processors had become bus bound meaning they could process information faster it could get into or out of the chip, so it was time for a change.
Remember i mentioned processors only having one interface to the outside world. Way back when processors performed memory read and write cycles on the same bus as much slower I/O (yes I/O devices, even if they where memory mapped!) You may have also noticed some incredible leaps in memory technology over the last ten years. It's like the people holding all the Alien technology has forgotten More's law.
So it was time for a change. the processor's could out pace their data while the memory chips could supply the processors data needs, but didn't a transport mechanism, so the front side bus was born. Dedicated to memory interfacing it could be tailored especially to meet the higher data bandwidth requirements, because it didn't have to share with all of the slower devices in the system.
As for who named it Front Side, I don't know. Probably someone at a memory company who thought it appropriate, because all the other *** was going in and out o0f the other side of the chip.
Hope this helps, I can't keep my eyes epen any longer.