That, and all the other good reasons: simple repairs, ready spare parts availability, avoiding vendor lock-in for the product or any spare parts. 700 - 1,000 USD seems possible. (And I’m not sure about the prices of the Indian-made models, they are probably more expensive than the advertised ~2500 USD.)
A major reason is also that the roaster would be designed for 16 hours of unattended operation per day. Commercial roasters are only as large and expensive as they are (often 30-300 kg per batch) to get fixed cost degradation for the human worktime involved. That changes when the machine can roast on its own batch after batch – then, the machine can also be smaller and cheaper.
It seems that this new paradigm of small but automated machinery has not yet arrived in the roaster business world. So we need to either retrofit an existing drum-type roaster with automatic feeding and pouring and electronic control tech, or design our own. Not sure yet, but I’m not keen on the work of designing an own roaster just yet.