The ROI is the most important.
I look at how long it takes for the machine to produce what it cost me. Now, if it's more than 9 months, I don't buy.
Several of my latest machines did not produce the BTC they cost me. Because of the low reliability of bitmain machines, the increase in difficulty, plus import taxes, it's hard.
If a machine that costs 0.1BTC only produces in it's working life 0.08BTC, there is no reason to buy it, it is better to keep the money.
I don't know how other miners do it, but for me in Europe it's no longer profitable, even with free electricity.
The issue is, if manufacturers released cheap powerful machines, the difficulty would just sky rocket even further, by a lot.
It became unprofitable a long time ago when machines needed to consume 1kW+ of power. The electricity cost in Europe is insane. The only way to do it profitably is to either have a mass amount of solar power and battery storage, or somehow have free electricity from some other form of renewable power, which realistically, how many people live next to a river/stream or has a wind turbine?