BITCOIN -why antminer manufacturer don't keep the computer

If I buy Antminer S5 in amazon and install in a cheap energy country(kwh 0.09 USD), I would pay the investment in 8 months. Probably, the factory and amazon has a profit. The shipping cost, delay to receive payment etc...

So, why Antminer owner sell his miner/computers ? ps:Don't expect a next generation.