When you have 90% of the market share entering the price war affects the market leader the most.Intel got the best cost structure of any semiconductor company. Because they can afford designs that got higher utilization rates. Intel is the only company in the world that got lower transistor cost at 14nm. You can only lose against them in a price war.
How much do you think Ryzen would sell if it had the same price as the competing 6900K? Not very much, there is literally no reason to switch to AMD if Intel offers same perf/watt. This means AMD has to price their products lower.
Chasing AMD to the bottom would hurt Intel more than letting AMD take its marketshare back.
Same reason why Nvidia doesn't lower 1060 6gb price to under $200. They totally could (it's cheaper to manufacture than the rx480), but it makes them less money if they do that, because 1060gb already outsells rx480 2:1.
Similarly Intel has the mindshare. They have to be more careful not to canibalize their own margin by entering the price war with AMD. AMD has no marketshare, they got nothing to lose. Only way for them with Ryzen is up.