Why would the money dry up when we have companies willing to spend $1000/developer/month on AI tooling when they would have balked at $5/u/mo for some basic tooling 2-3 years ago?

First in some cases it is more than $1000/dev/month.

Those companies spending 1000+/developer are doing it with the same hope that at some point those $1000/month will replace the developer salary per month. Or because by doing so more investors will put more money into them.

Take away the promise of AI replacing developers and see how much a company is willing to pay for LLMs. It is not zero as there are very good cases for coding assisted by LLM or agentic engineering.