Because as it’s written it specifically indicates it’s a financial move: give Broadcom more money for more chips.

As you wrote it, it could be an IP partnership, Apple opening a fab, or something else.

It's much more specific. "Spend" would increase Broadcom's revenue. "Partners with" might be anything: investment, R&D assistance, whatever.

Both are public companies so they might be required to reveal these details

In English (is it worse in American English?) we frequently convert gerunds into simpler forms of the word. The spending turns into the spend. Related,the request turns into the ask (although this example turns out to have a strong anglo saxon linguistic bias).

I hear this frequently in the US business community, as an alternative to "spending".

It's gramatically correct, spend is a noun here (but you expected a verb).

https://en.wiktionary.org/wiki/spend#Noun

It sounds off because “increase” can be a verb or a noun and “spend” can also be used as a verb or a noun (but is more often used as a verb) so you’re brain is trying to parse the sentence with dual meaning terms

It sounds better on the quarterly report than "Apple will pay more money"

Your proposed sentence contains less information.

The initial headline also conveys both that there is current spend with Broadcom, and that the future spend is higher than current levels.

"spend" as a noun is a linguistic differentiator to indicate what a badass MBA program you attended.

Help pump AVGO by tipping sentiment and creating a visualization of billions getting dumped into Broadcom.

I think it just means they had been partnering in the past and now they're expanding it with more investment.

That's an ask for Apple, not us ;)