Arguments in favour of belt drive argue around issues of strength, never needing to carry a spare chain, no maintenance requirement, and silent oil-free operation.
I will acknowledge, they are (allegedly) quieter in use. Steel is pretty damn strong and while my chain needs to be lubed, the Purple Extreme keeps the chain remarkably oil-free. On many long touring rides I have never needed to carry a spare chain, rarely needed to carry out any major maintenance, just re-lube every 600-1000kms. Belt-drive is a solution looking for a problem IMHO.