Nothing is forever, not even giant companies. It is well known that companies grow, plateau, and fade or disappear.
In the short term, the Fortune top 10 US companies in 2022 saw seven new entrants and seven exits compared to 2012. This is not unique to the tech era. Churn is the norm decade after decade.
In the long run, most large companies at a given time are gone a hundred years later. Bought by others, faded to relative anonymity, or bankrupt.