Timing belt is one from the most expensive engine parts. On the other hand, your fan belt or serpentine belt is cheaper one. If you have been little mechanical or have interest in mechanics. Possibly you have seen working of your belt. If all these are yes, you have your answer.
Timing belt replacement cost is so high because it is the main part that runs your machine. It synchronizes your crankshaft and camshaft. These small rubber tooth links crankshaft timing gear with camshaft timing gear. Timing belt tensioner is used to tighten it. Mechanic tights it to ensure proper working and let not a single tooth slip or jump. It is responsible to open & close your engine at proper timing.
Do you ever want to buy a low priced low quality product that can increase and decrease your engine life? Obviously No. You do not want to risk your car of thousands dollars for few dollars. Sometimes if timing belt is not replaced on specific change interval and breaks on road can cause your major accidents and also engine rebuilt. Engine rebuilt is multiple times costly than belt replacement cost.
Did you ever recommend some service or product to someone? Yes we do consciously and unconsciously without letting the person know. Most of the good mechanics think the same way. They choose best quality to get free marketing efforts from your end. You pay for quality.
What is cost of your car? Just assume 50,000 is your car price. On average timing belt price starts from 250 dollars (depending upon car model/made). It is not even 1% of total cost. Think like you are Audi owner. Do you want to sacrifice your brand trust? Would you like to get complaints? Not at all.
I hope you have answer of your question. TIA 🙂