Do software patents only exist for rich players to build a moat against poorer players? At this point with patents of this quality only reason for them to exist seems to be to cross-license them for extra revenue and to possibly block anyone too poor to fight for themselves...

Almost all these patents exist as a war chest and a deterrent against other companies. Everyone theoretically perpetually infringes on each other's obscure patents all the time, but there is a detente between the big players because they hold the gun to each other's heads. If you as a small guy enter the game, you're just shot.

Economically, it’s to avoid free-rider effects. This benefit largely seems alien to tech people because the industry inherently has other moats: network effects, data and code in a server instead of a product sold to consumers that competitors can easily disassemble and reverse engineer, etc.

Precisely the reason is to give breathing room for big players to invest in development of technology so they can capitalise exclusively for a period

They exist so you can not be forbidden to do what you invented.. but there might be unintended correlation ;)

I don't disagree, but Mistral is hardly a "rich player" in the current AI bubble.

OpenAI, Anthropic, Google, Meta and X are each valued at a trillion or more. Mistral is valued at $20B, 50x less. Even Deepseek is several times bigger than Mistral.