Similar to certain banks in 2007/2008, the idea would be “so much investment is tied to one company that if that company went bankrupt, it could have consequences for the broader economy”
The thing is, it is not 2007/2008 any more. The US government is holding record amounts of debt and countries around the world are now trying to become independent of it. This includes its bond markets on which the dollar relies upon to give it its reserve currency status, which in turn is what gives it its power to print money and bail industries out. If something happens that requires Big Tech to be bailed out and international bond holders decide the US is no longer reliable, it could very well end up triggering the collapse of the US dollar as the world's reserve currency and the downfall of the US as we know it.
Not to mention, there’s also that tariffs thing going on.