For some context on the costs, SEC analysis for 2017–2020 puts the median figure at $750k, and the mean is over double, $1.8 million.[1] In more recent years, the costs have only grown. Despite being theoretically possible to run one for less than $10k if you basically just provide the minimum legally required notice, in practice anything like that is very unlikely to actually succeed, and median (mean) costs have been $1.1m ($1.2m) in 2022 and $1.0m ($2.7m).[2] That's just the costs directly involved in proxy fights themselves, there are also often other things that you might like to do to improve chances of success.

Of course, even with the high costs, there are notable successes, such as Exxon having a quarter of their board replaced in 2021. And union organising is not mutually exclusive, in fact, Starbucks unions are seeking three seats on the board this year. But they're notable because of how rare they are, and the difficulties will mean that it's likely to remain relatively rare.

On the other hand, having the precedent set that it's even at all possible does probably make it more likely for directors to acquiesce to even non-binding resolutions.

[1]: https://corpgov.law.harvard.edu/2022/05/25/the-cost-of-proxy...

[2]: https://www.kirkland.com/publications/kirkland-manda-update/...