That plus the fact that the the major tech players (Amazon, FB, Google, MSFT, Netflix) are in a stronger competitive position now than they were previously. Ten stocks make up 23% of the US market and because  they make up such a large percentage of the overall market that their relative outperfromance keeps the indices from crashing. This article explains it well:

This is just a thought experiment but what if big tech continued to hold up if any of these various scenarios came to fruition? How much would the rest of the market have to fall if the market begins to crash again but big tech only experiences 60% of the total losses?

I’m completely pulling this 60% number out of thin air but this shows if the 10 biggest tech stocks continue to outperform on a relative basis, everything else would have to get crushed for the market to fall further.