That's because the tech industry has more money than god and nothing better to do with it.

Microsoft alone has half a trillion dollars in assets, and Apple/Google/Meta/Amazon are in similar financial positions. Spending a few tens of billions on datacenters is, as crazy as it sounds, nothing to them.

While ARPANET itself reportedly cost somewhere between 10 - 20 million USD, which is relatively cheap, the precursor research that allowed the internet to take off - which is directed more at general computing and advanced computer networks, the telecommunications investments - cost many billions of dollars, it was mostly public money is the biggest difference.

That said, private companies are pumping alot of money into this space, but technological progress is a peaks and valley situation. I imagine most of the money will ultimately move the needle very little following things of dubious hindsight value