There's a lot of different crypto algorithms. Some will work better on AMD, some on Nvidia, some regardless of memory and some dependant on large cache. A miner will benchmark their card against the popular algos and choose the most profitable one. Which is one of the main complaints when Nvidia limited ETH algos, that miners would just switch to ZHash with a percentage or two less profitability and thus it would do nothing about the shortage while possibly triggering false-positives for gamers.